OTNS

[spinel] do not update the sent frame if the frame has been updated b… #1550

Job	Run time
Unittests	3m 21s
Stress network-forming	24m 28s
Examples	2m 57s
Stress commissioning	14m 50s
Stress connectivity	16m 29s
Stress network-latency	3m 2s
Stress multicast-performance	2m 44s
Stress otns-performance	2m 53s
upload-coverage	23s
	1h 11m 7s

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