Fix/acl for forward (#1305)

Fix ACL on routed traffic and code refactor

client/firewall/manager/routerpair.go

@@ -0,0 +1,18 @@
+package manager
+
+type RouterPair struct {
+	ID          string
+	Source      string
+	Destination string
+	Masquerade  bool
+}
+
+func GetInPair(pair RouterPair) RouterPair {
+	return RouterPair{
+		ID: pair.ID,
+		// invert Source/Destination
+		Source:      pair.Destination,
+		Destination: pair.Source,
+		Masquerade:  pair.Masquerade,
+	}
+}