quickfix for IPv6, added basic documentation to the default configs

I have added a workaround for #5590 and some basic documentation for salt's IPv6 capability in the default config files. I left the former parameter to SREQ as a comment for an easy revert to String.format(), because I feel an IPv6 adress should be written to self.opts with brackets already present.
But as I do not know the further implications of changing formats in opts, this puts IPv6 in a usable state for now.