LU-6261 gnilnd: kgnilnd_check_rdma_cq race in error path.

LU-6261 gnilnd: kgnilnd_check_rdma_cq race in error path.

It is possible for multiple threads to both be processing a
transaction error that causes the connection to close.
If the close path stalls after changing the conn state to CLOSING,
the tx_done path will put a tx in purgatory since the conn state is
not ESTABLISHED anymore. When the close path continues, it expects to
find that the conn->gnc_mdd_list is empty and assert if it isn't
empty.
Change the error code for the tx_done path so that we don't put this
tx in purgatory since we are closing the connection anyway.

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: I4458522f16508eb53d380f62320c65c7bf84657a
Reviewed-on: http://review.whamcloud.com/15439
Tested-by: Jenkins
Reviewed-by: James Shimek <jshimek@cray.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>