ipv6: use ->ndo_tunnel_ctl in addrconf_set_dstaddr

Use the new ->ndo_tunnel_ctl instead of overriding the address limit
and using ->ndo_do_ioctl just to do a pointless user copy.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>