krbd, kcephfs: trash osd primary-affinity

libceph.ko support is in testing and should be in 3.15.  This commit
effectively reverts commit 66ffaa65657b ("kcephfs, krbd: do not thrash
primary-affinity").

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>