[6.12.3] Unraid Custom Network: br0 Ipv6 detect wrong in some cases

As this post points that 

The docker script will use $IPV6(2409:xxxx:xxxx:5ee0::4b8/128) to get $SUBNET6(2409:xxxx:xxxx:5ee0::/64) via ip -6 route show dev $NETWORK $IPV6|awk '{print $1;exit}'

It will case $SUBNET6 be null, and $GATEWAY6 always be 1 —— So that it leads to br0: ipv6 is disabled in docker network inspect.