[tests] Fix network interface tests for Android 30 (#4868)

Context: https://developer.android.com/preview/behavior-changes-11#netlink-mac
Context: https://developer.android.com/reference/java/net/NetworkInterface#getNetworkInterfaces()

If an application targets Android 11/API-30 (and later), then the
number of reported network interfaces as well as the amount of
information about those interfaces includes less detail.

First of all, only interfaces with associated IP addresses will be
reported by both the `NetworkInterface` Java API and the
[**getifaddrs**(3)][0] native libc API:

  * Application targetting API-28 on API-30 device:
      * name: wlan0; type: Ethernet
      * name: dummy0; type: Ethernet
      * name: lo; type: Loopback
      * name: hwsim0; type: Unknown
      * name: ip6tnl0; type: Tunnel
      * name: sit0; type: Tunnel
      * name: ip6_vti0; type: Tunnel
      * name: ip_vti0; type: Tunnel
  * Application targetting API-30 on API-30 device:
      * name: wlan0; type: 0
      * name: dummy0; type: 0
      * name: lo; type: 0

Second of all, as can be seen above, device information does not
include the type of interface.  This bit of information is what the
`DotNetInterfacesShouldEqualJavaInterfaces()` test relied on so far.

That change breaks `DotNetInterfacesShouldEqualJavaInterfaces()`:

	DotNetInterfacesShouldEqualJavaInterfaces
	Mono interfaces:
	  [InterfaceInfo: Name=radio0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::d4d9:5aff:fe48:60be%11, fec0::d4d9:5aff:fe48:60be, fec0::397c:d582:6278:ca2c, 10.0.2.15>]
	  [InterfaceInfo: Name=wlan0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::e00a:8bb6:415b:4c97%9, fec0::f925:950b:4c31:eea7, fec0::315a:4cc4:796:6915, 10.0.2.16>]
	  [InterfaceInfo: Name=dummy0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::4c41:86ff:fe93:6354%2>]
	  [InterfaceInfo: Name=lo, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<::1, 127.0.0.1>]
	Java interfaces:
	  [InterfaceInfo: Name=dummy0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::4c41:86ff:fe93:6354%2>]
	  [InterfaceInfo: Name=wlan0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::e00a:8bb6:415b:4c97%9, fec0::f925:950b:4c31:eea7, fec0::315a:4cc4:796:6915, 10.0.2.16>]
	  [InterfaceInfo: Name=lo, IsLoopback=True, IsUp=True, HardwareAddress=<>, Addresses=<::1, 127.0.0.1>]
	  [InterfaceInfo: Name=radio0, IsLoopback=False, IsUp=True, HardwareAddress=<>, Addresses=<fe80::d4d9:5aff:fe48:60be%11, fec0::d4d9:5aff:fe48:60be, fec0::397c:d582:6278:ca2c, 10.0.2.15>]
	Interface radio0: passed
	Interface wlan0: passed
	Interface dummy0: passed
	[FAIL] :   #8.3 (lo not found in Java interfaces)
	   Expected: True
	   But was:  False
	     at System.NetTests.NetworkInterfacesTest.DotNetInterfacesShouldEqualJavaInterfaces ()
	     at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
	     at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)

Note that both Java and Mono return the same number of interfaces, with
the same names, but the `lo` interface in Mono list is not marked as a
loopback (`IsLoopback=False`), while the corresponding Java entry
reports the interface is a loopback.

In order to account for the above Android changes, we now look not only
at the hardware type but also at its name in order to determine whether
the device is a loopback one or not.

[0]: https://www.man7.org/linux/man-pages/man3/getifaddrs.3.html

Author: grendello

src/Mono.Android/Test/System.Net/NetworkInterfaces.cs

@@ -170,7 +170,7 @@ bool IsInterfaceUp (MNetworkInterface inf)
 
 				default:
 					// Android considers 'lo' to be always up
-					return inf.NetworkInterfaceType == NetworkInterfaceType.Loopback;
+					return IsLoopbackInterface (inf);
 			}
 		}
 
@@ -188,9 +188,10 @@ byte[] GetHardwareAddress (MNetworkInterface inf)
 			var ret = new List <InterfaceInfo> ();
 
 			foreach (MNetworkInterface inf in interfaces) {
+				Console.WriteLine ($"inf: {inf} (name: {inf.Name}; type: {inf.NetworkInterfaceType})");
 				ret.Add (new InterfaceInfo {
 					Name = inf.Name,
-					IsLoopback = inf.NetworkInterfaceType == NetworkInterfaceType.Loopback,
+					IsLoopback = IsLoopbackInterface (inf),
 					IsUp = IsInterfaceUp (inf),
 					HardwareAddress = GetHardwareAddress (inf),
 					Addresses = CollectAddresses (inf)
@@ -220,5 +221,12 @@ byte[] GetHardwareAddress (MNetworkInterface inf)
 
 			return ret;
 		}
+
+		static bool IsLoopbackInterface (MNetworkInterface inf)
+		{
+			// Android 30 will not tell us the interface type if the app targets API 30, we need to look at the
+			// name then.
+			return inf.NetworkInterfaceType == NetworkInterfaceType.Loopback || String.Compare ("lo", inf.Name, StringComparison.OrdinalIgnoreCase) == 0;
+		}
 	}
 }