improve documentation of templates used in GGSN_Tests

Various improvements to the comments documenting packet templates
used in GGSN_Tests: fix IPv4 vs. IPv6 confusion, clearly indicate
whether templates are used for sending or for receiving/matching
packets, and add a missing comment.

Found while studying code to prepare for issue OS#2519.

Change-Id: I3bfc21a5ba74e0505457e4874f93501ad7c68b7b
Related: OS#2519
1 file changed