LU-1693 obdfilter: Set bi_rw before calling bio_add_page()

LU-1693 obdfilter: Set bi_rw before calling bio_add_page()

In filter_do_bio() set bi_rw before calling bio_add_page()
so that the correct bio direction is used in mgrge_bvec_fn().

port of master patch 79badd39c6584ae136b14d919eaf699ee812b666

Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: Ib43a5c198db691f8ed4001c41af7b984a264922b
Reviewed-on: http://review.whamcloud.com/4765
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>