Floss: force update |ConnectionHandler::feature_map_|

Absolute volume support relies on the result of |SdpLookup|, and is
stored in |ConnectionHandler::feature_map_|.

However, it is possible that the result is stored as "unsupported" in a
bad connection that doesn't get cleaned up properly (e.g., due to
missing "Connection Closed Event"), in which case the next connection
will inherit that result even when its |SdpLookup| finds
"supported", due to the use of |std::map::emplace|.

In this CL, we force the updates so the states sync better, assuming
there is no good reason to do such permissive update.

Bug: 254313937
Test: Deploy and verify absolute volume is correctly propagated after a
bad connection-disconnection
Tag: #floss

Change-Id: Ia634df6cd36dc17e0486391ff462d37bfc61ada6