net: dsa: fix reference counting for LAG FDBs

Due to an invalid conflict resolution on my side while working on 2
different series (LAG FDBs and FDB isolation), dsa_switch_do_lag_fdb_add()
does not store the database associated with a dsa_mac_addr structure.

So after adding an FDB entry associated with a LAG, dsa_mac_addr_find()
fails to find it while deleting it, because &a->db is zeroized memory
for all stored FDB entries of lag->fdbs, and dsa_switch_do_lag_fdb_del()
returns -ENOENT rather than deleting the entry.

Fixes: c2693363 ("net: dsa: request drivers to perform FDB isolation")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20220723012411.1125066-1-vladimir.oltean@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/switch.c

@@ -344,6 +344,7 @@ static int dsa_switch_do_lag_fdb_add(struct dsa_switch *ds, struct dsa_lag *lag,
 
 	ether_addr_copy(a->addr, addr);
 	a->vid = vid;
+	a->db = db;
 	refcount_set(&a->refcount, 1);
 	list_add_tail(&a->list, &lag->fdbs);