mlxsw: spectrum_router: Add extack argument to mlxsw_sp_lb_rif_init()

The extack will be handy in later patches.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Link: https://lore.kernel.org/r/e87ba300121010d580b80a281877573a7b1377ca.1687438411.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>