[PATCH] IB: fix userspace CM deadlock

Fix deadlock condition resulting from trying to destroy a cm_id
from the context of a CM thread.  The synchronization around the
ucm context structure is simplified as a result, and some simple
code cleanup is included.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>