[automerger skipped] Merge "Stop prefix discovery if an RA prefix arrives in DISCOVERING" into rvc-dev am: a314315001 -s ours

am skip reason: Change-Id I3803fa3d9806848b331c35ee8bac256934bd1f21 with SHA-1 d8911baa45 is in history

Change-Id: Ia03b25467390136e847f1ecde7e4f1cbe5ee6451