CAP based ipv6 in docker

Hi Dominic,

You may find these changes interesting.
I tried to be more granular in granting caps to the dockerized process & then I went further by forcing the inner shell to forfeit these added capabilites.
This solution is still not perfect as it is forbidding me to ping6 (need for NET_RAW_SOCKET).

Thank you for the original work, I couldn't find much on Docker on IPv6.

Cheers,
Boris.