[diag] Handle errors of `TransmitPacket()` #14

Job	Run time
packet-verification-1-1-on-1-4	12m 3s
packet-verification-low-power	8m 51s
thread-1-4-gcc-m32	11m 37s
channel-manager-csl	3m 5s
thread-1-4-gcc-m64	13m 17s
expects	31m 20s
thread-1-4-posix	10m 4s
thread-1-4-clang-m32	9m 42s
thread-1-4-clang-m64	9m 57s
upload-coverage	0s
	1h 49m 56s

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