RDMA/cma: Fix synchronization with device removal in cma_iw_handler

RDMA/cma: Fix synchronization with device removal in cma_iw_handler

The cma_iw_handler needs to validate the state of the rdma_cm_id before
processing a new connection request to ensure that a device removal is
not already being processed for the same rdma_cm_id.  Without the state
check, the user can receive simultaneous callbacks for the same cm_id, or
a callback after they've destroyed the cm_id.

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