mlxsw: spectrum_router: Add support for VRFs

Allow port netdevs, LAG and VLAN devices stacked on top of these to be
enslaved to a VRF master device.

Upon enslavement, create a router interface (RIF) for the enslaved
netdev and associate it with a virtual router (VR) based on the VRF's
table ID.

If a RIF already exists for the netdev (f.e., due to the existence of an
IP address), then it's deleted and a new one is created with the
appropriate VR binding.

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