Fix IPv6 route steering traffic

Fixes #28327

This patch stops adding /64 route to the cilium_net iface, which brought all the traffic to local node. When using something like /120 per node and having pods within the same /64 as the node meant that no cross-node traffic from pods worked.

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

pkg/datapath/loader/netlink.go

@@ -432,6 +432,7 @@ func addHostDeviceAddr(hostDev netlink.Link, ipv4, ipv6 net.IP) error {
 				IP:   ipv6,
 				Mask: net.CIDRMask(64, 128), // corresponds to /64
 			},
+			Flags: unix.IFA_F_NOPREFIXROUTE,
 		}
 
 		if err := netlink.AddrReplace(hostDev, &addr); err != nil {