Support for XLink Kai 'DDS' integration

[CrunchBite]

With the recent work and merging of #3782 this is the ideal time to add support for directly exchanging LAN traffic with XLink Kai for online play. This can be accomplished with a UDP socket and a small handshake process then PCSX2 will be able to exchange Ethernet frames. (Using a proper PS2/Sony MAC address)
I added this feature to XLink Kai a couple versions ago and at the same time added support to Dolphin in dolphin-emu/dolphin#8853
I've written a short spec doc on 'DDS' here: https://www.teamxlink.co.uk/wiki/DDS_Protocol

XLink Kai DDS serves three purposes:

1. Communication with other remote players over internet (Emulated or real consoles!)
2. Communication with other emulators connected to the same XLink Kai client
3. Communication with physical consoles on the local LAN

From a PCSX2 user's perspective they'll need the option to choose whether to use this or not, and will need the ability to configure the IP address of the XLink Kai client to connect to (default to localhost).

[CrunchBite]

I've expanded the DDS documentation a bit. Added the auto-discovery mechanism and added a compatibility matrix.
https://www.teamxlink.co.uk/wiki/DDS_Protocol

[GovanifY]

Thank you @CrunchBite ! I'll try to take a look at it soon, work has been hitting me hard last week

[CrunchBite]

No worries! Gives me more time to build an adequate test setup :)

[MasonT8198]

Is this still in the plans?

[GovanifY]

Yes, it is! I and the team have just been quite busy as of late and we had to prioritize big work lately. Hopefully we will be able to work on this soon, otherwise anyone willing to do so in the meantime can always submit a patch, ping me, and I'll review it!