Bump third_party/openthread/repo from `aed9cd1` to `c519aa4` #340

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	1h 58m 15s
Build on Linux (gcc_debug)	1h 1m 4s
Build on Linux (python_lib)	29m 1s
Build on Darwin (clang, python_lib, simulated)	1h 54m 0s
Build on Linux (coverage)	14m 1s
Build on Linux (python lighting-app)	6m 8s
	5h 42m 29s

Provide feedback