Add support for Connector loopback testing for Ethernet #39479

Job	Run time
build (base)	4m 36s
build (clang)	4m 24s
autotest (sitltest-rover)	18m 6s
autotest (sitltest-sailboat)	2m 38s
autotest (sitltest-balancebot)	7m 58s
	37m 42s

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