mlxsw: spectrum_router: Move IPIP init up

mlxsw will need to keep track of certain devices that are not related to
any of its front panel ports. This includes IPIP netdevices. To be able to
query the list of supported IPIP types, router->ipip_ops_arr needs to be
initialized.

To that end, move the IPIP initialization up (and finalization
correspondingly down).

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>