bridge: Allow deleting FDB entries with non-existent VLAN

It is currently impossible to delete individual FDB entries (as opposed
to flushing) that were added with a VLAN that no longer exists:

 # ip link add name dummy1 up type dummy
 # ip link add name br1 up type bridge vlan_filtering 1
 # ip link set dev dummy1 master br1
 # bridge fdb add 00:11:22:33:44:55 dev dummy1 master static vlan 1
 # bridge vlan del vid 1 dev dummy1
 # bridge fdb get 00:11:22:33:44:55 br br1 vlan 1
 00:11:22:33:44:55 dev dummy1 vlan 1 master br1 static
 # bridge fdb del 00:11:22:33:44:55 dev dummy1 master vlan 1
 RTNETLINK answers: Invalid argument
 # bridge fdb get 00:11:22:33:44:55 br br1 vlan 1
 00:11:22:33:44:55 dev dummy1 vlan 1 master br1 static

This is in contrast to MDB entries that can be deleted after the VLAN
was deleted:

 # bridge vlan add vid 10 dev dummy1
 # bridge mdb add dev br1 port dummy1 grp 239.1.1.1 permanent vid 10
 # bridge vlan del vid 10 dev dummy1
 # bridge mdb get dev br1 grp 239.1.1.1 vid 10
 dev br1 port dummy1 grp 239.1.1.1 permanent vid 10
 # bridge mdb del dev br1 port dummy1 grp 239.1.1.1 permanent vid 10
 # bridge mdb get dev br1 grp 239.1.1.1 vid 10
 Error: bridge: MDB entry not found.

Align the two interfaces and allow user space to delete FDB entries that
were added with a VLAN that no longer exists:

 # ip link add name dummy1 up type dummy
 # ip link add name br1 up type bridge vlan_filtering 1
 # ip link set dev dummy1 master br1
 # bridge fdb add 00:11:22:33:44:55 dev dummy1 master static vlan 1
 # bridge vlan del vid 1 dev dummy1
 # bridge fdb get 00:11:22:33:44:55 br br1 vlan 1
 00:11:22:33:44:55 dev dummy1 vlan 1 master br1 static
 # bridge fdb del 00:11:22:33:44:55 dev dummy1 master vlan 1
 # bridge fdb get 00:11:22:33:44:55 br br1 vlan 1
 Error: Fdb entry not found.

Add a selftest to make sure this behavior does not regress:

 # ./rtnetlink.sh -t kci_test_fdb_del
 PASS: bridge fdb del

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Andy Roulin <aroulin@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20241105133954.350479-1-idosch@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>