clatd: move stop_loop() into main.c am: 8ab7e13332 am: 2c2543395c am: 246713b634

Original change: https://android-review.googlesource.com/c/platform/external/android-clat/+/1574002

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I391595e70475b4314fce6ebe0e980bc9126fbb2a