mlxsw: spectrum_router: Update multipath hash parameters upon netevents

Make sure the device and the kernel are performing the multipath hash
according to the same parameters by updating the device whenever the
relevant netevent is generated.

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