[IPV6]: Fix address/interface handling in UDP and DCCP, according to the scoping architecture.

TCP and RAW do not have this issue.  Closes Bug #7432.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>