Bring back the older mmulti revision from EDuke32-OldMP

Striker had some problems with the newer revision of mmulti, so he reverted to an older one for EDuke32-OldMP. IPv6 support is lost, while Windows XP support is resurrected, at least in theory. There's also the NatFree option from AddFaz that I'm still not sure about.

One side-effect of this is that the command-line syntax for starting up a P2P game is reverted to the syntax of older revisions of JFDuke3D and JFSW, as well as all releases of EDuke32-OldMP using this older mmulti revision.