enable the ipv6 flag in podman network to be able to create
dual-stack networks for containers.
This is required to be compatible with docker, where --ipv6
really means dual stack.
podman, unlike docker, support IPv6 only containers since
07e3f1bba9674c0cb93a0fa260930bfebbf75728.
Signed-off-by: Antonio Ojea <aojea@redhat.com>