When neigh_init fails, we have to do proper cleanup including
router_fini call.

Fixes: 6cf3c971 ("mlxsw: spectrum_router: Add private neigh table")
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Acked-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>