net/packet: add IPv6 source and destination IPs to Parsed.

Signed-off-by: David Anderson <danderson@tailscale.com>

net/packet/ip6.go

@@ -0,0 +1,24 @@
+package packet
+
+import (
+	"fmt"
+
+	"inet.af/netaddr"
+)
+
+type IP6 [16]byte
+
+func IP6FromNetaddr(ip netaddr.IP) IP6 {
+	if !ip.Is6() {
+		panic(fmt.Sprintf("IP6FromNetaddr called with non-v6 addr %q", ip))
+	}
+	return IP6(ip.As16())
+}
+
+func (ip IP6) Netaddr() netaddr.IP {
+	return netaddr.IPFrom16(ip)
+}
+
+func (ip IP6) String() string {
+	return ip.Netaddr().String()
+}