configs/releng/airootfs/etc/xdg/reflector/reflector.conf: use mirrors that support both IPv4 & IPv6

This ensures that IPv6-only systems get working mirrors.

CHANGELOG.rst

@@ -15,6 +15,7 @@ Changed
 -------
 
 - Mount /etc/pacman.d/gnupg on ramfs instead of tmpfs to ensure its contents never land in swap.
+- Configure reflector to return only mirrors that support both IPv4 and IPv6.
 
 Removed
 -------

configs/releng/airootfs/etc/xdg/reflector/reflector.conf

 # Reflector configuration file for the systemd service.
 
 --save /etc/pacman.d/mirrorlist
+--ipv4
+--ipv6
 --protocol https
 --latest 20
 --sort rate