kclient: dosync in writepages if sync_mode is WB_SYNC_ALL
kclient: dosync in writepages if sync_mode is WB_SYNC_ALL

If we dosync if !pdflush, then we end up doing syncs from
balance_dirty_pages, wreaking havoc on the OSDs.

It's possible the current_is_pdflush() check isn't needed at all..

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph