LU-791 obdfilter: Don't clear OBD_MD_FLFLAGS mistakenly

LU-791 obdfilter: Don't clear OBD_MD_FLFLAGS mistakenly

Instead of set oa->o_valid to OBD_MD_FLID | OBD_MD_FLGROUP arbitrarily
in filter_handle_precreate(), it should be changed as "|=" to keep
the OBD_MD_FLFLAGS setted in filter_precreate().

Otherwise, client will not be aware of OST is running out of space,
and lov_create() will wait for objects forever in such case.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I84be8dde59dbb2829cd800e10b7aa6f4402b7e56
Reviewed-on: http://review.whamcloud.com/1589
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: hongchao.zhang <hongchao.zhang@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>