ceph: fix message revocation

A message can be on a queue (pending or sent), or out_msg (sending), or
both.  We were assuming that if it's not on a queue it couldn't be out_msg,
but that was false in the case of lossy connections like the OSD.  Fix
ceph_con_revoke() to treat these cases independently.  Also, fix the
out_kvec_is_message check to only trigger if we are currently sending
_this_ message.

This fixes a GPF in tcp_sendpage, triggered by OSD restarts.

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