ipv6: addrlabel: remove refcounting

After previous patch ("ipv6: addrlabel: rework ip6addrlbl_get()")
we can remove the refcount from struct ip6addrlbl_entry,
since it is no longer elevated in p6addrlbl_get()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>