mlxsw: spectrum: router: Squash the default route table to main

Currently, the mlxsw Spectrum driver offloads only either the RT_TABLE_MAIN
FIB table or the VRF tables, so the RT_TABLE_LOCAL table is squashed to the
RT_TABLE_MAIN table to allow local routes to be offloaded too.

By default, multicast MFC routes which are not assigned to any user
requested table are put in the RT_TABLE_DEFAULT table.

Due to the fact that offloading multicast MFC routes support in Spectrum
router logic is going to be introduced soon, squash the default table to
MAIN too.

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