Remove DHCPv6, use leasetime from interface (#4507)

Signed-off-by: Omoeba <38597972+Omoeba@users.noreply.github.com>

advanced/Scripts/webpage.sh

@@ -440,7 +440,7 @@ dhcp-leasefile=/etc/pihole/dhcp.leases
             echo "#quiet-dhcp6
 #enable-ra
 dhcp-option=option6:dns-server,[::]
-dhcp-range=::100,::1ff,constructor:${interface},ra-names,slaac,64,3600
+dhcp-range=::,constructor:${interface},ra-names,ra-stateless,64
 ra-param=*,0,0
 " >> "${dhcpconfig}"
         fi