net: dsa: assign a bridge number even without TX forwarding offload

The service where DSA assigns a unique bridge number for each forwarding
domain is useful even for drivers which do not implement the TX
forwarding offload feature.

For example, drivers might use the dp->bridge_num for FDB isolation.

So rename ds->num_fwd_offloading_bridges to ds->max_num_bridges, and
calculate a unique bridge_num for all drivers that set this value.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 9606e56..4901cdc 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -152,7 +152,9 @@ unsigned int dsa_bridge_num_get(const struct net_device *bridge_dev, int max)
 	unsigned int bridge_num = dsa_bridge_num_find(bridge_dev);
 
 	if (!bridge_num) {
-		/* First port that offloads TX forwarding for this bridge */
+		/* First port that requests FDB isolation or TX forwarding
+		 * offload for this bridge
+		 */
 		bridge_num = find_next_zero_bit(&dsa_fwd_offloading_bridges,
 						DSA_MAX_NUM_OFFLOADING_BRIDGES,
 						1);