classifier: Remove internal mutex.

classifier: Remove internal mutex.

Almost all classifier users already exclude concurrent modifications,
or are single-threaded, hence the classifier internal mutex can be
removed.  Due to this change, ovs-router.c and tnl-ports.c need new
mutexes, which are added.

As noted by Ben in review, ovs_router_flush() should also free the
entries it removes from the classifier.  It now calls
ovsrcu_postpone() to that effect.

Suggested-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>