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

Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Change-Id: Ife34d5d89337ea7fea41b5844fd724211b05c670
Reviewed-on: http://review.whamcloud.com/3501
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>