MAVProxy does not work with IPv6

[rotu]

MAVProxy does not work when the host is specified as an IPv6 address.

When trying to open MAVProxy with IPv6, argument parsing is broken:

e.g. sim_vehicle.py "--out=udp:[::]:14550"

"UDP ports must be specified as host:port"

Also the socket connection code uses socket.AF_INET instead of socket.AF_INET6 so it will not use IPv6 even if the parsing is corrected.