[diag] Handle errors of `TransmitPacket()` #16

Job	Run time
channel-manager-csl	3m 22s
packet-verification-1-1-on-1-4	11m 17s
packet-verification-low-power	8m 56s
thread-1-4-gcc-m32	11m 26s
thread-1-4-gcc-m64	11m 1s
thread-1-4-clang-m32	10m 32s
expects	31m 25s
thread-1-4-clang-m64	9m 31s
thread-1-4-posix	10m 1s
upload-coverage	0s
	1h 47m 31s

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