mlxsw: spectrum_router: Export IPv6 link local address check helper

Neighbors with link local addresses are not offloaded to the host table,
yet, the are maintained in the driver for adjacency table usage. When
dumping the IPv6 host neighbors this link local neighbors should be
ignored. This patch exports this helper for dpipe usage.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>