Print hexdumps with offset instead of address

Print hexdumps with offset instead of address. This change is
done to be able to use the wcn36xx-dissector wireshark plugin
available here:
https://github.com/kanstrup/wcn36xx-dissector

Signed-off-by: Mikael Kanstrup <mikael.kanstrup@gmail.com>
Merge pull request #59 from kanstrup/dissector

Print hexdumps with offset instead of address