Bugfix, plot ack_rtt

plot_transmission_timeline.py

     )
 
     # remove all not needed columns
-    transmission_df = transmission_df.filter(["goodput", "datetime"])
+    transmission_df = transmission_df.filter(["goodput", "datetime", "ack_rtt"])
 
     # read serial csv
     serial_df = pd.read_csv(args.serial_file)