mlxsw: spectrum: Add dummy FID initialization

For forwarding using ACL action, HW needs a valid FID to be setup. It
does not actually use it, so it can be any valid FID. So create a dummy
FID only for this purpose.

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