fix extended fuse bits for ethernet board

Forgot to fix ethernet board in previous commit

Author: descampsa

hardware/arduino/avr/boards.txt

@@ -456,7 +456,7 @@ ethernet.upload.speed=115200
 ethernet.bootloader.tool=avrdude
 ethernet.bootloader.low_fuses=0xff
 ethernet.bootloader.high_fuses=0xde
-ethernet.bootloader.extended_fuses=0x05
+ethernet.bootloader.extended_fuses=0xFD
 ethernet.bootloader.file=optiboot/optiboot_atmega328.hex
 ethernet.bootloader.unlock_bits=0x3F
 ethernet.bootloader.lock_bits=0x0F