ipv6: rearm router solicitaion timer when setting new tokenized address

When a new tokenized address gets installed we send out just one
router solicition. We should send out `rtr_solicits' in case one router
advertisment got lost.

So, rearm the timer as we do in addrconf_dad_complete.

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>