RDMA/nes: Use atomic counters for CM listener create and destroy

After running long iterative MPI tests, sometimes ethtool reports a
"CM Destroy Listener" count more than the "CM Create Listener" count.
This inconsistency is fixed by making counter variables atomic.

Signed-off-by: Faisal Latif <faisal.latif@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>