Bump third_party/openthread/repo from `f0b6fce` to `e19c775` #1208

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2h 8m 59s
Build on Linux (fake, gcc_release, clang, simulated)	2h 14m 48s
Build on Linux (coverage)	16m 14s
Build on Linux (gcc_debug)	1h 18m 10s
Build on Linux (python_lib)	32m 46s
Build on Linux (python lighting-app)	10m 10s
	6h 41m 7s

Provide feedback