LU-1571 mdt: Do not update xid for open replay req

LU-1571 mdt: Do not update xid for open replay req

Do not update last_xid for open replay req,
otherwise the following resend(after replay)
can not be matched with correct xid.

Remove unnecessary mti_transo zero check in
mdt_empty_transno.

Signed-off-by: wang di <di.wang@whamcloud.com>
Change-Id: I2a05f3ac05b301ae31641a1dc51f8c4eed96427d
Reviewed-on: http://review.whamcloud.com/3195
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>