Cisco ASA generator has no way to enable ipv6 address processing

Hi, I came across a curious bug(?) in the Cisco ASA generator, where the code seems to have hardcoded that it only processes ipv4 addresses, although the support for ipv6 is also there and it works, as long as the hardcoded part is modified a bit. A bug, unfinished feature, or intentionally left unused (why?)? I could see the Cisco ASA generator utilizing same header keys as the Cisco generator here to optionally process ipv6 also.

Passing the address family should happen here, but since it is omitted, the default value of 4 is always used: https://github.com/google/capirca/blob/master/capirca/lib/ciscoasa.py#L342