ceph: close old con before reopening on mds reconnect

When we detect a mds session reset, close the old ceph_connection before
reopening it.  This ensures we clean up the old socket properly and keep
the ceph_connection state correct.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>
(cherry picked from commit a53aab645c82f0146e35684b34692c69b5118121)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>