RDMA/cma: Reenable device removal on passive side

Enable conn_id remove on the passive side after connection
establishment.  This corrects an issue where the IB driver can't be
unloaded after running applications over RDS.  The 'dev_remove' counter
does not reach 0 for established connections on the passive side.

This problem is limited to device removal, and only occurs on the
passive side if there are established connections.

Signed-off-by: Vladimir Sokolovsky <vlad@mellanox.co.il>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>