IB/core: Map iWarp AH type to undefined in rdma_ah_find_type

iWarp devices do not support the creation of address handles
so return AH_ATTR_TYPE_UNDEFINED for all iWarp devices.

While we are here reduce the size of port_num to u8 and add
a comment.

Fixes: 44c58487d51a ("IB/core: Define 'ib' and 'roce' rdma_ah_attr types")
Reported-by: Parav Pandit <parav@mellanox.com>
CC: Sean Hefty <sean.hefty@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/rdma/ib_verbs.h

@@ -874,6 +874,7 @@ struct ib_mr_status {
 __attribute_const__ enum ib_rate mult_to_ib_rate(int mult);
 
 enum rdma_ah_attr_type {
+	RDMA_AH_ATTR_TYPE_UNDEFINED,
 	RDMA_AH_ATTR_TYPE_IB,
 	RDMA_AH_ATTR_TYPE_ROCE,
 	RDMA_AH_ATTR_TYPE_OPA,
@@ -3810,17 +3811,24 @@ static inline void rdma_ah_set_grh(struct rdma_ah_attr *attr,
 	grh->traffic_class = traffic_class;
 }
 
-/*Get AH type */
+/**
+ * rdma_ah_find_type - Return address handle type.
+ *
+ * @dev: Device to be checked
+ * @port_num: Port number
+ */
 static inline enum rdma_ah_attr_type rdma_ah_find_type(struct ib_device *dev,
-						       u32 port_num)
+						       u8 port_num)
 {
 	if (rdma_protocol_roce(dev, port_num))
 		return RDMA_AH_ATTR_TYPE_ROCE;
-	else if ((rdma_protocol_ib(dev, port_num)) &&
-		 (rdma_cap_opa_ah(dev, port_num)))
-		return RDMA_AH_ATTR_TYPE_OPA;
-	else
+	if (rdma_protocol_ib(dev, port_num)) {
+		if (rdma_cap_opa_ah(dev, port_num))
+			return RDMA_AH_ATTR_TYPE_OPA;
 		return RDMA_AH_ATTR_TYPE_IB;
+	}
+
+	return RDMA_AH_ATTR_TYPE_UNDEFINED;
 }
 
 /**