On HP/UX, the structs used by ioctl(SIOCGLIFCONF) are named differently

On HP/UX, the structs used by ioctl(SIOCGLIFCONF) are named differently
than on other platforms, and only IPv6 addresses are returned. Because of
those two issues, fall back to ioctl(SIOCGIFCONF) on HP/UX, so that it at
least compiles and finds IPv4 addresses. This function is currently only
used for interpreting samehost/samenet in pg_hba.conf, which isn't that
critical.