ceph: remove unused erank field

The ceph_entity_addr erank field is obsolete; remove it.  Get rid of
trivial addr comparison helpers while we're at it.

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

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

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

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

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