This is checking for the following order of operations, and makes sure
to deny that configuration:

ip link add link swp2 name swp2.100 type vlan id 100
ip link add br0 type bridge vlan_filtering 1
ip link set swp2 master br0
bridge vlan add dev swp2 vid 100

Instead of using vlan_for_each(), which looks at the VLAN filters
installed with vlan_vid_add(), just track the 8021q uppers. This has the
advantage of freeing up the vlan_vid_add() call for actual VLAN
filtering.

There is another change in this patch. The check is moved in slave.c,
from switch.c. I don't think it makes sense to have this 8021q upper
check for each switch port that gets notified of that VLAN addition
(these include DSA links and CPU ports, we know those can't have 8021q
uppers because they don't have a net_device registered for them), so
just do it in slave.c, for that one slave interface.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>