mlxsw: spectrum_router: Pass struct mlxsw_sp_rif_params to fid_get

The fid_get callback is called to allocate a FID for the newly-created RIF.
In a following patch, the fid_get implementation for VLANs will be modified
to take the VLAN ID from the parameters instead of deducing it from the
netdevice. To that end, propagate the RIF parameters to the fid_get
callback.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>