software/ors-amarisoft: Do not give RU more than /64
Dnsmasq insists on dhcp-range's prefixlen to be at most 64, which triggers the following error if original slaptap is wider than that:
dnsmasq: prefix length must be at least 64 at line 5 of /srv/slapgrid/slappart6/etc/dnsmasq.cfg
-> Fix it by capping provided range to /64
/reported-by @lu.xu
/cc @jhuge, @tomo, @xavier_thompson, @Daetalus