[diag] Handle errors of `TransmitPacket()` #17

Job	Run time
channel-manager-csl	3m 4s
expects	31m 42s
packet-verification-1-1-on-1-4	11m 15s
packet-verification-low-power	8m 48s
thread-1-4-gcc-m32	11m 49s
thread-1-4-posix	9m 56s
thread-1-4-gcc-m64	11m 23s
thread-1-4-clang-m32	10m 2s
thread-1-4-clang-m64	9m 47s
upload-coverage	19s
	1h 48m 5s

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