What does GPL3 license mean in the context of Wssdl? That if I write a dissector with it then it has to be open sourced?
This is nothing new though: all wireshark plugins must be GPL, since the API itself they rely on is GPL.
EDIT: I'm not entirely correct There are provisions for the network situation ("ASP (application service provider) loophole") I described, but I looks like it's not necessarily the default mode. See [0][1].
[0] https://en.wikipedia.org/wiki/GNU_General_Public_License
[1] https://en.wikipedia.org/wiki/Affero_General_Public_License
As Wikipedia notes, some drafts of the GPLv3 contained such a provision, but this did not make it into the final version.