mlxsw: spectrum: Handle VLAN device unlinking

In commit 993107fe

 ("mlxsw: spectrum_switchdev: Fix VLAN device
deletion via ioctl") I fixed a bug caused by the fact that the driver
views differently the deletion of a VLAN device when it is deleted via
an ioctl and netlink.

Instead of relying on a specific order of events (device being
unregistered vs. VLAN filter being updated), simply make sure that the
driver performs the necessary cleanup when the VLAN device is unlinked,
which always happens before the other two events.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>