Describe XDP option in help

packet-exchange/src/server.c

@@ -83,7 +83,7 @@ struct timespec measures_start;
 struct timespec measures_end;
 
 static void help(char *argv[]) {
-  printf("Usage: %s [-aghtv] [-b CLIENT_IP] [-d BUF_LEN] [-f IF] [-i USEC] [-p PRIO] [-r USEC]\n\n", argv[0]);
+  printf("Usage: %s [-aghtv] [-b CLIENT_IP] [-d BUF_LEN] [-f IF] [-i USEC] [-p PRIO] [-r USEC] [-x]\n\n", argv[0]);
   printf("       -a                    Run the real time thread on CPU1\n");
   printf("       -b CLIENT_IP          Server side RTT\n");
   printf("       -d BUF_LEN            Set the length of tx buffer\n");
@@ -95,6 +95,7 @@ static void help(char *argv[]) {
   printf("       -r USEC               Refresh the non real time main thread every USEC microseconds\n");
   printf("       -t                    Enable timestamps\n");
   printf("       -v                    Verbose\n");
+  printf("       -x                    Use AF_XDP sockets\n");
   printf("\n");
 }