I wasn't sure if this script comes from Debian or Xen or somewhere else,
so I thought it safest to report it here.

IPv6 on the Dom0 should be removed from switched/bridged interfaces.
Earlier I would just sysctl disable_ipv6 on the interface, but the below
diff seems to remove the link local address too. I've attached the full
fixed file as well.

*** xen-network-common.sh.orig  2024-03-19 11:53:17.000000000 +0200
--- xen-network-common.sh       2024-03-19 11:59:38.000000000 +0200
***************
*** 95,100 ****
--- 95,101 ----
       fi

       # ... and configure it
+     ip link set dev ${dev} addrgenmode none
       ip address flush dev ${dev}
   }