libceph: fix CEPH_FEATURE_CEPHX_V2 check in calc_signature()

Upstream commit cc255c76 ("libceph: implement CEPHX_V2 calculation
mode") was adjusted incorrectly: CEPH_FEATURE_CEPHX_V2 if condition got
inverted, thus breaking 4.9.144 and later kernels for all setups that
use cephx.

Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/auth_x.c

@@ -804,7 +804,7 @@ static int calc_signature(struct ceph_x_authorizer *au, struct ceph_msg *msg,
 	void *enc_buf = au->enc_buf;
 	int ret;
 
-	if (msg->con->peer_features & CEPH_FEATURE_CEPHX_V2) {
+	if (!(msg->con->peer_features & CEPH_FEATURE_CEPHX_V2)) {
 		struct {
 			__le32 len;
 			__le32 header_crc;