mlxsw: spectrum: Add support for VLAN devices on top of LAG

When creating a VLAN device on top of LAG, we are basically creating a
vPort on top of each of the port netdevs member in the LAG. Therefore,
these vPorts should inherit both the LAG status and LAG ID from the
underlying port netdevs.

In addition, when the VLAN device joins or leaves a bridge each of the
underlying vPorts should know about it and act accordingly. This is
achieved by propagating the VLAN event down to the lower devices.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>