Stop clat if it's no longer in use.

Normally, clatd is stopped when a connection disconnects.
However, if the connection's LinkProperties change, or if the
disconnect somehow gets lost (e.g., because of bug 8486114),
then we need to stop it (and possibly restart it).

Bug: 8276725
Change-Id: Ib8ad0d653ed8d0cd70b7414bcaa8fdaef8ba5fcc