IB/cm: Check cm_id state before handling a REP

Move checking the state of a cm_id before modifying it when handling a
REP.  This fixes a bug seen under MPI scale-up testing, where a NULL
timewait_info pointer is dereferenced if a request times out before a
REP is received.

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