Follow-up fix for fwmark 101b5564c267e673afdea97e24a6bd778939abd8 (#372)

Remove all FwMark settings from client configs (illegal) and QRcode
(also illegal).

model/client.go

@@ -30,6 +30,5 @@ type ClientData struct {
 type QRCodeSettings struct {
 	Enabled       bool
 	IncludeDNS    bool
-	IncludeFwMark bool
 	IncludeMTU    bool
 }