LU-759 mdc: Clear rq_replay on error in mdc_enqueue()

LU-759 mdc: Clear rq_replay on error in mdc_enqueue()

When mdc_enter_request() fails (e.g., due to signals) in mdc_enqueue(),
the request is freed without any care about its rq_replay field.  For
rq_replay requests, this results in assertion failures in
__ptlrpc_free_req().  This patch adds a call to mdc_clear_replay_flag()
to make sure __ptlrpc_free_req()'s assumption is respected.

Change-Id: I2185066a9f47b3d9563d9e1a8989754ef2e2dcb4
Signed-off-by: Li Wei <liwei@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1518
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>