net: dsa: check VLAN capability of every switch

Now that the VLAN object is propagated to every switch chip of the
switch fabric, we can easily ensure that they all support the required
VLAN operations before modifying an entry on a single switch.

To achieve that, remove the condition skipping other target switches,
and add a bitmap of VLAN members, eventually containing the target port,
if we are programming the switch target.

This will allow us to easily add other VLAN members, such as the DSA or
CPU ports (to introduce cross-chip VLAN support) or the other port
members if we want to reduce hardware accesses later.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>