title: Pyshark - duplicate fields not printed using cap[0].ip._all_fields_
body: <p>I'm using pyshark to read pcap and convert it into dataframe for further analysis.
  In data - say layer1 has attribute named 'data' which is repeated -data can contain 1,2,3 values. While using <code>cap[0].layer1._all_fields()</code> method I only get single entries of data column. But normal <code>pretty_print()</code> displays multiple values.
  Is there a workaround for it?
  Thanks</p>