libceph: store session key in cephx authorizer

Session key is required when calculating message signature. Save the session
key in authorizer, this avoid lookup ticket handler for each message

Signed-off-by: Yan, Zheng <zyan@redhat.com>

net/ceph/auth_x.h

@@ -26,6 +26,7 @@ struct ceph_x_ticket_handler {
 
 
 struct ceph_x_authorizer {
+	struct ceph_crypto_key session_key;
 	struct ceph_buffer *buf;
 	unsigned int service;
 	u64 nonce;