Fix nix builds: go dependencies are awful

netforward/netforward.go

@@ -0,0 +1,20 @@
+// From https://github.com/goburrow/netforward
+package netforward
+
+import (
+	"net"
+)
+
+// Dialer dials to a remote address.
+type Dialer interface {
+	Dial() (net.Conn, error)
+}
+
+func IsPacketNetwork(network string) bool {
+	switch network {
+	case "udp", "udp4", "udp6", "ip", "ip4", "ip6", "unixgram":
+		return true
+	default:
+		return false
+	}
+}