ipv6: remove old token ipv6 address as soon as possible

If the tokenized ip address is re-set on an interface we depend on the
arrival of a new router advertisment to call addrconf_verify to clean
up the old address (which valid_lft is now set to 0). Old addresses can
linger around for a longer time if e.g. the source of router advertisments
vanishes.

So, call addrconf_verify immediately after setting the new tokenized
address to get rid of the old tokenized addresses.

Cc: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>