xprtrdma: treat all calls not a bcall when bc_serv is NULL

(git-fixes).

suse-commit: 09657ad2ed0a957b8ff945e2b48bd6035b7f84a4

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -1120,6 +1120,7 @@ static bool
 rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
 #if defined(CONFIG_SUNRPC_BACKCHANNEL)
 {
+	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
 	struct xdr_stream *xdr = &rep->rr_stream;
 	__be32 *p;
 
@@ -1143,6 +1144,10 @@ rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
 	if (*p != cpu_to_be32(RPC_CALL))
 		return false;
 
+	/* No bc service. */
+	if (xprt->bc_serv == NULL)
+		return false;
+
 	/* Now that we are sure this is a backchannel call,
 	 * advance to the RPC header.
 	 */