libceph: split osdmap allocation and decode steps

Split osdmap allocation and initialization into a separate function,
ceph_osdmap_decode().

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>

diff --cc include/linux/ceph/osdmap.h
Simple merge

diff --cc net/ceph/osd_client.c
Simple merge

diff --cc net/ceph/osdmap.c
Simple merge