Fix IPv6 route on cilium_host iface

Fixes #28327

This patch fixes the subnet assigned to the cilium_host device from /64 back to
/128, a bug introduced in ecd4fc0 when
converting the init.sh script to Go code. The conversion never meant to change
the behavior in init.sh and the bug caused connectivity issues in certain cilium
configurations.

Signed-off-by: Ashley Reese <ashley@victorianfox.com>

pkg/datapath/loader/netlink.go

@@ -430,7 +430,7 @@ func addHostDeviceAddr(hostDev netlink.Link, ipv4, ipv6 net.IP) error {
 		addr := netlink.Addr{
 			IPNet: &net.IPNet{
 				IP:   ipv6,
-				Mask: net.CIDRMask(64, 128), // corresponds to /64
+				Mask: net.CIDRMask(128, 128), // corresponds to /128
 			},
 		}