ceph: decode updated mdsmap format

The mds map now uses the global_id as the 'key' (instead of the addr,
which was a poor choice).

This is protocol change.

Signed-off-by: Sage Weil <sage@newdream.net>

diff --cc fs/ceph/ceph_fs.h
Simple merge

diff --cc fs/ceph/mdsmap.c
Simple merge

diff --cc fs/ceph/mdsmap.h
Simple merge