OTNS

use `kMinCslIePeriod` #248

Job	Run time
Examples	3m 40s
Stress network-forming	22m 21s
Stress commissioning	19m 57s
Stress connectivity	16m 24s
Stress network-latency	4m 11s
Stress multicast-performance	3m 22s
Stress otns-performance	4m 8s
Unittests	4m 45s
upload-coverage	18s
	1h 19m 6s

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