SVN does not have any IPv6 configuration files. I've been answering
this SVNKit question for years in various forum and AFAIK changing the
JVM option works. This is a low level JVM thing not what the higher
level libraries use and from what I recall SVNKit just uses the
built-in JVM network function regardless.
Either way, this is a question for the TMate forums and if they are
not answering questions there is only so much we can do as none of us
have ever contributed to their library in any way.