[infiniband] Generate more specific errors in response to failure MADs

Generate errors within individual MAD transaction consumers such as
ib_pathrec.c and ib_mcast.c, rather than within ib_mi.c.  This allows
for more meaningful error messages to eventually be displayed to the
user.

src/net/infiniband/ib_mcast.c

@@ -86,6 +86,8 @@ static void ib_mcast_complete ( struct ib_device *ibdev,
 	unsigned long qkey;
 
 	/* Report failures */
+	if ( ( rc == 0 ) && ( mad->hdr.status != htons ( IB_MGMT_STATUS_OK ) ))
+		rc = -ENOTCONN;
 	if ( rc != 0 ) {
 		DBGC ( ibdev, "IBDEV %p QPN %lx join failed: %s\n",
 		       ibdev, qp->qpn, strerror ( rc ) );