ceph: record updated mon_addr on remount

Note that the new monitors are just shown in /proc/mounts.
Ceph does not (re)connect to new monitors yet.

[ jlayton: s/printk\(KERN_NOTICE/pr_notice(/
	   s/strcmp/strcmp_null/ ]

Signed-off-by: Venky Shankar <vshankar@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>