[ip6] do not report an error for disabled host loopback #32

Job	Run time
channel-manager-csl	12m 4s
expects	30m 27s
packet-verification-1-1-on-1-3	10m 46s
packet-verification-low-power	9m 29s
thread-1-3-gcc-m32	10m 21s
thread-1-3-posix	8m 33s
thread-1-3-gcc-m64	10m 38s
thread-1-3-clang-10-m32	10m 2s
thread-1-3-clang-10-m64	9m 31s
upload-coverage	24s
	1h 52m 15s

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