Bump third_party/openthread/repo from `f0b6fce` to `5e34ab2` #1562

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2h 21m 53s
Build on Linux (fake, gcc_release, clang, simulated)	2h 10m 49s
Build on Linux (gcc_debug)	1h 16m 18s
Build on Linux (python_lib)	31m 40s
Build on Linux (python lighting-app)	10m 44s
Build on Linux (coverage)	16m 38s
	6h 48m 2s

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