Fixed top-level message field msg_dir to be optional

openair2/ENB_APP/MESSAGES/V2/progran.proto

@@ -5,7 +5,7 @@ import "stats_messages.proto";
 import "header.proto";
 
 message progran_message {
-       required progran_direction msg_dir = 100;
+       optional progran_direction msg_dir = 100;
 	oneof msg {
               prp_hello hello_msg = 1;
               prp_echo_request echo_request_msg = 2;