staging: lustre: ptlrpc: race at req processing

Fix: 5c689e68 ("staging/lustre/ptlrpc: race at req processing")
decreased the race window, but does not remove it. Disable rq_resend
right after MSG_REPLAY flag set. Import lock protects two threads
from race between set/clear MSG_REPLAY and rq_resend flags.

Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5554
Xyratex-bug-id: MRP-1888
Reviewed-on: http://review.whamcloud.com/10735


Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>