RDMA/nes: Fix crash in nes_accept()

While running IMP_EXT's window test, we saw a crash in nes_accept().
Here is the sequence of what happened:

(1) In MVAPICH2, connect request is received for port #0.

FIX:  Add a nes_connect() check to make sure local or remote tcp port
      is not 0.

(2) Remote node's (passive) TCP stack sends a reset when it gets a
    connect request because of port = 0.  Active side set the connect
    error to IW_CM_EVENT_STATUS_REJECTED when it received the RST from
    remote node.

FIX: The corect error code is -ECONNRESET.

(3) Wrong error code of IW_CM_EVENT_STATUS_REJECTED causes the core to
    destroy its listener ports.  Here there are connections that may
    have sent an MPA request up and waiting for accept or reject.  But
    the listener and its cm_nodes have been freed already causing the
    crash noticed.

FIX: The cm_node is freed only if its state is not
     NES_CM_STATE_MPAREQ_RCVD.  If cm_node's state is
     NES_CM_STATE_MPAREQ_RCVD then its new state is set to
     NES_CM_STATE_LISTENER_DESTROYED and it is not freed.  When
     nes_accept() or nes_reject() is received, its state is checked
     for NES_CM_STATE_LISTENER_DESTROYED and in this case the cm_node
     is freed and error is returned.

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