Auto merge of #2991 - SteveLauC:extattr_list_xx-on-NetBSD, r=JohnTitor

add extattr_list_xxx() on NetBSD

Corresponds to [this](https://github.com/NetBSD/src/blob/ac36f3f9fee8aff1c69d653503149faaa531f752/sys/sys/extattr.h#L98-L103):
```c
ssize_t	extattr_list_fd(int _fd, int _attrnamespace, void *_data,
	    size_t _nbytes);
ssize_t	extattr_list_file(const char *_path, int _attrnamespace, void *_data,
	    size_t _nbytes);
ssize_t	extattr_list_link(const char *_path, int _attrnamespace, void *_data,
	    size_t _nbytes);
```

Author: bors

libc-test/semver/netbsd.txt

@@ -1538,3 +1538,6 @@ basename
 XATTR_CREATE
 XATTR_REPLACE
 EXTATTR_NAMESPACE_EMPTY
+extattr_list_fd
+extattr_list_file
+extattr_list_link

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -2459,6 +2459,24 @@ extern "C" {
         envp: *const *const ::c_char,
     ) -> ::c_int;
 
+    pub fn extattr_list_fd(
+        fd: ::c_int,
+        attrnamespace: ::c_int,
+        data: *mut ::c_void,
+        nbytes: ::size_t,
+    ) -> ::ssize_t;
+    pub fn extattr_list_file(
+        path: *const ::c_char,
+        attrnamespace: ::c_int,
+        data: *mut ::c_void,
+        nbytes: ::size_t,
+    ) -> ::ssize_t;
+    pub fn extattr_list_link(
+        path: *const ::c_char,
+        attrnamespace: ::c_int,
+        data: *mut ::c_void,
+        nbytes: ::size_t,
+    ) -> ::ssize_t;
     pub fn extattr_delete_fd(
         fd: ::c_int,
         attrnamespace: ::c_int,