mlxsw: spectrum: Move L3 protocol and address definitions to global header file

The L3 protocol and address definitions are going to be used by the NVE
code, so move them to the global header file from the one private to the
router.

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