Proxy: Avoid log error.  Simplify locking.

Don't log an error when Accept failed because the interface (portal)
was just removed.

Don't pass around a pointer to a serviceInfo since another thread
deletes those.  Instead, just check if service name is still in the
service map.

Delete the locking on the serviceInfo object since it is only used
by the "main" proxier thread.
Merge pull request #2697 from erictune/no_accept_err

Proxy: Avoid log error.  Simplify locking.