net: mscc: ocelot: allow forwarding from bridge ports to the tag_8021q CPU port

Currently we are unable to ping a bridge on top of a felix switch which
uses the ocelot-8021q tagger. The packets are dropped on the ingress of
the user port and the 'drop_local' counter increments (the counter which
denotes drops due to no valid destinations).

Dumping the PGID tables, it becomes clear that the PGID_SRC of the user
port is zero, so it has no valid destinations.

But looking at the code, the cpu_fwd_mask (the bit mask of DSA tag_8021q
ports) is clearly missing from the forwarding mask of ports that are
under a bridge. So this has always been broken.

Looking at the version history of the patch, in v7
https://patchwork.kernel.org/project/netdevbpf/patch/20210125220333.1004365-12-olteanv@gmail.com/
the code looked like this:

	/* Standalone ports forward only to DSA tag_8021q CPU ports */
	unsigned long mask = cpu_fwd_mask;

(...)
	} else if (ocelot->bridge_fwd_mask & BIT(port)) {
		mask |= ocelot->bridge_fwd_mask & ~BIT(port);

while in v8 (the merged version)
https://patchwork.kernel.org/project/netdevbpf/patch/20210129010009.3959398-12-olteanv@gmail.com/
it looked like this:

	unsigned long mask;

(...)
	} else if (ocelot->bridge_fwd_mask & BIT(port)) {
		mask = ocelot->bridge_fwd_mask & ~BIT(port);

So the breakage was introduced between v7 and v8 of the patch.

Fixes: e21268efbe ("net: dsa: felix: perform switch setup for tag_8021q")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20210817160425.3702809-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mscc/ocelot.c

@@ -1334,6 +1334,7 @@ void ocelot_apply_bridge_fwd_mask(struct ocelot *ocelot)
 			struct net_device *bond = ocelot_port->bond;
 
 			mask = ocelot_get_bridge_fwd_mask(ocelot, bridge);
+			mask |= cpu_fwd_mask;
 			mask &= ~BIT(port);
 			if (bond) {
 				mask &= ~ocelot_get_bond_mask(ocelot, bond,