Remove namespace from ContentPacketExtension

[jahndis]

This commit sets the namespace of the ContentPacketExtension to null. This was causing issues when parsing the jingle session-initiate message with stanza.io. The namespace was being set on content elements inside a group which stanza.io would fail to parse.

According the group XEP there usually isn't a namespace on the content elements (https://xmpp.org/extensions/xep-0338.html), and the namespace currently doesn't show up on the content elements inside the jingle element in the session-initiate message. (smack 4.2 might be doing something smart to remove a child element's namespace if it is the same as the parent).

More details in this discussion: https://community.jitsi.org/t/jitsi-dev-custom-client-fails-to-parse-jingle-session-initiate-with-new-jicofo/13992

Ran tests in jitsi-videobridge, jicofo, jicoco, and jigasi and all passed.

[damencho]

@bgrozev @bbaldino WDYT?
I think this is safe and this was the way it used to be prior smack4 update.

[bbaldino]

so do we not need to set the namespace based on its usage? (i.e. ingo's comment here)

[damencho]

Yep, I'm not sure about that.
But if smack is removing namespace when they match the parent as @jahndis reported,
then defining two namespaces in ContentPacketExtension and make namespace as a required constructor parameter and passing the correct one depending on the usage will be a better approach. WDYT?
@jahndis can you try that?

[bgrozev]

How does this affect parsing?

[ibauersachs]

• Smack doesn't do much in this case, since we're generating the XML ourselves (see AbstractPacketExtension.java#L123)
• Parsing isn't affected if the namespace matches the namespace of the outer element (i.e. it is redundant)
• It's causing issues for XEP-0338 because the namespace is not redundant, but simply the wrong one (not that a namespace is present at all)

Regardless, could you please make some changes?

• Remove the NAMESPACE field entirely, having it like this is confusing
• Pass null into the constructor, like it was before c7affc2

[jahndis]

Sorry for the delay in response. I was sick for a couple days and then on vacation through the rest of the week.

I made the changes you recommended, and reran the tests (all passed). Let me know if there's anything else needed.

[ibauersachs]

Note that the other projects need to update the version of Jitsi-Desktop that is referenced in their pom.xml. You might want to open separate pull requets for that or wait until another change will pull things in.