Bump third_party/openthread/repo from `aed9cd1` to `d7810fa` #297

Job	Run time
Build on Darwin (clang, python_lib, simulated)	1h 45m 3s
Build on Linux (coverage)	13m 34s
Build on Linux (fake, gcc_release, clang, simulated)	1h 59m 3s
Build on Linux (gcc_debug)	1h 2m 54s
Build on Linux (python_lib)	29m 10s
Build on Linux (python lighting-app)	11m 26s
	5h 41m 10s

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