LU-5554 ptlrpc: race at req processing

LU-5554 ptlrpc: race at req processing

First commit 56e5a6bb4fc0329092f85016b8664da0b6ffa8a8
decrease 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>
Xyratex-bug-id: MRP-1888
Change-Id: I64d7c997976ff73956ebe97d7ea0775e0a54bc50
Reviewed-on: http://review.whamcloud.com/10735
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>