mlxsw: spectrum: Don't create FIDs upon creation of VLAN uppers

Up until now we used to create FIDs upon the creation of VLAN uppers on
top of the VLAN-aware bridge. This was done so that in case a router
interface (RIF) was configured on top of the bridge, the FID would
already be there.

Instead, simplify the code and only create the FID upon RIF creation.

This is an intermediary step towards the introduction of the common FID
core, in which this code would be completely removed.

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>