lncli: use original snake_case names for JSON serializing

Because we now use printRespJSON everywhere where we print RPC
responses as JSON, we can simply instruct the jsonpb marshaler to
use the original snake_case name specified in the proto file for
the JSON field names and not the default camelCase.

cmd/lncli/commands.go

@@ -57,6 +57,7 @@ func printJSON(resp interface{}) {
 func printRespJSON(resp proto.Message) {
 	jsonMarshaler := &jsonpb.Marshaler{
 		EmitDefaults: true,
+		OrigName:     true,
 		Indent:       "    ",
 	}