[PATCH] IB: Add user-supplied context to userspace CM ABI

- Add user specified context to all uCM events.  Users will not retrieve
  any events associated with the context after destroying the corresponding
  cm_id.
- Provide the ib_cm_init_qp_attr() call to userspace clients of the CM.
  This call may be used to set QP attributes properly before modifying the QP.
- Fixes some error handling synchonization and cleanup issues.
- Performs some minor code cleanup.

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