ceph: touch existing cap when handling reply

Move cap to tail of session->s_caps list. So ceph_trim_caps() will
trim older caps first.
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -657,6 +657,10 @@ void ceph_add_cap(struct inode *inode,
 		session->s_nr_caps++;
 		spin_unlock(&session->s_cap_lock);
 	} else {
+		spin_lock(&session->s_cap_lock);
+		list_move_tail(&cap->session_caps, &session->s_caps);
+		spin_unlock(&session->s_cap_lock);
+
 		if (cap->cap_gen < session->s_cap_gen)
 			cap->issued = cap->implemented = CEPH_CAP_PIN;