whisper: add light mode check to handshake (#16725)

cmd/utils/flags.go

@@ -567,6 +567,10 @@ var (
 		Usage: "Minimum POW accepted",
 		Value: whisper.DefaultMinimumPoW,
 	}
+	WhisperRestrictConnectionBetweenLightClientsFlag = cli.BoolFlag{
+		Name:  "shh.restrict-light",
+		Usage: "Restrict connection between two whisper light clients",
+	}
 
 	// Metrics flags
 	MetricsEnabledFlag = cli.BoolFlag{
@@ -1099,6 +1103,9 @@ func SetShhConfig(ctx *cli.Context, stack *node.Node, cfg *whisper.Config) {
 	if ctx.GlobalIsSet(WhisperMinPOWFlag.Name) {
 		cfg.MinimumAcceptedPOW = ctx.GlobalFloat64(WhisperMinPOWFlag.Name)
 	}
+	if ctx.GlobalIsSet(WhisperRestrictConnectionBetweenLightClientsFlag.Name) {
+		cfg.RestrictConnectionBetweenLightClients = true
+	}
 }
 
 // SetEthConfig applies eth-related command line flags to the config.