Unify environment var readers

proxy/freedom/freedom.go

@@ -41,7 +41,7 @@ func init() {
 		return h, nil
 	}))
 	const defaultFlagValue = "NOT_DEFINED_AT_ALL"
-	value := platform.NewEnvFlag("xray.buf.splice").GetValue(func() string { return defaultFlagValue })
+	value := platform.NewEnvFlag(platform.UseFreedomSplice).GetValue(func() string { return defaultFlagValue })
 	switch value {
 	case "auto", "enable":
 		useSplice = true