ipv6: don't add link local route when there is no link local address

When an address is added on loopback (ip -6 a a 2002::1/128 dev lo), a route
to fe80::/64 is added in the main table:
  unreachable fe80::/64 dev lo  proto kernel  metric 256  error -101

This route does not match any prefix (no fe80:: address on lo). In fact,
addrconf_dev_config() will not add link local address because this function
filters interfaces by type. If the link local address is added manually, the
route to the link local prefix will be automatically added by
addrconf_add_linklocal().
Note also, that this route is not deleted when the address is removed.

After looking at the code, it seems that addrconf_add_lroute() is redundant with
addrconf_add_linklocal(), because this function will add the link local route
when the link local address is configured.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>