Changes goodput calculation.

plot_transmission_timeline.py

     print(transmission_df)
 
     # key for columns and level for index
-    print(transmission_df["payload_size"].groupby(pd.Grouper(level="datetime", freq="{}s".format(args.interval))).sum().dropna())
-    #print(transmission_df["goodput"])
+    goodput_df = transmission_df["payload_size"].groupby(pd.Grouper(level="datetime", freq="{}s".format(args.interval))).sum().dropna()
+    print(goodput_df)
     exit()