threadnetwork: Avoid execute command if service does not exist am: 0afad08ea2

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3343649

Change-Id: I49499989692fda16b2d92daa42c0d68ba3388ded
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>