[connman] introduce: retrieve inet6 interface name and index

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[connman] implement retrieve inet6 interface name and index

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[connman] dnsproxy: fetch inet6 ifname if AF_INET6

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[connman] ofono plugin: fix ipv6 support

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
Merge pull request #30 from jpoutiai/cellular_IPV6

Cellular ipv6