RDMA/nes: Allocate work item for disconnect event handling

The code currently has a work structure in the QP.  This requires a
lock and a pending flag to ensure there is never more than one request
active.  When two events happen quickly (such as FIN and LLP CLOSE),
it causes unnecessary timeouts since the second one is dropped.

This fix allocates memory for the work request so the second one can
be queued.  A lock is removed since it is no longer needed.

Signed-off-by: Don Wood <donald.e.wood@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>