Add a function to dissect an E.164 (MSISDN) number in UTF8 format and use it
in the Diameter dissector.

This new API adds a filter for the MSISDN as well as a subtree and filter for
the Country Code.

Change-Id: Ibcbf4b5f72178b7e4af63efa7496188d608a9de7
Reviewed-on: https://code.wireshark.org/review/3760
Petri-Dish: Jeff Morriss <jeff.morriss.ws@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>