optional struct tag for SNAC(0x01,0x10) evil notif

Instead of having two separate structs for the evil notification
struct, we now have just one struct that leverages the optional
field to indicate whether the warning is anonymous or not.

foodgroup/icbm.go

@@ -233,19 +233,20 @@ func (s ICBMService) EvilRequest(ctx context.Context, sess *state.Session, inFra
 	}
 	recipSess.IncrementWarning(increase)
 
-	var notif any
+	notif := wire.SNAC_0x01_0x10_OServiceEvilNotification{
+		NewEvil: recipSess.Warning(),
+	}
+
+	// append info about user who sent the warning
 	if inBody.SendAs == 0 {
-		notif = wire.SNAC_0x01_0x10_OServiceEvilNotification{
-			NewEvil: recipSess.Warning(),
+		notif.Snitcher = &struct {
+			wire.TLVUserInfo
+		}{
 			TLVUserInfo: wire.TLVUserInfo{
 				ScreenName:   sess.DisplayScreenName().String(),
 				WarningLevel: sess.Warning(),
 			},
 		}
-	} else {
-		notif = wire.SNAC_0x01_0x10_OServiceEvilNotificationAnon{
-			NewEvil: recipSess.Warning(),
-		}
 	}
 
 	s.messageRelayer.RelayToScreenName(ctx, recipSess.IdentScreenName(), wire.SNACMessage{

foodgroup/icbm_test.go

@@ -391,7 +391,7 @@ func TestICBMService_EvilRequest(t *testing.T) {
 					FoodGroup: wire.OService,
 					SubGroup:  wire.OServiceEvilNotification,
 				},
-				Body: wire.SNAC_0x01_0x10_OServiceEvilNotificationAnon{
+				Body: wire.SNAC_0x01_0x10_OServiceEvilNotification{
 					NewEvil: evilDeltaAnon,
 				},
 			},
@@ -438,9 +438,13 @@ func TestICBMService_EvilRequest(t *testing.T) {
 				},
 				Body: wire.SNAC_0x01_0x10_OServiceEvilNotification{
 					NewEvil: evilDelta,
-					TLVUserInfo: wire.TLVUserInfo{
-						ScreenName:   "sender-screen-name",
-						WarningLevel: 110,
+					Snitcher: &struct {
+						wire.TLVUserInfo
+					}{
+						wire.TLVUserInfo{
+							ScreenName:   "sender-screen-name",
+							WarningLevel: 110,
+						},
 					},
 				},
 			},

wire/snacs.go

@@ -268,11 +268,11 @@ type SNAC_0x01_0x0F_OServiceUserInfoUpdate struct {
 
 type SNAC_0x01_0x10_OServiceEvilNotification struct {
 	NewEvil uint16
-	TLVUserInfo
-}
-
-type SNAC_0x01_0x10_OServiceEvilNotificationAnon struct {
-	NewEvil uint16
+	// Snitcher specifies the user who sent the warning. Nil pointer indicates
+	// an anonymous warning.
+	Snitcher *struct {
+		TLVUserInfo
+	} `oscar:"optional"`
 }
 
 type SNAC_0x01_0x11_OServiceIdleNotification struct {