mod_s2s: Fix logging of <stream:error> consistency with other mods `reason` was often a table, so the log said "table: 0xptr" or such. mod_c2s, mod_bosh etc logs the stream error stanza object, so better do the same. It would be nicer if this was an util.error object, but that will have to be a future change.

-- Unknown platform stub
module:set_global();

-- TODO Do things that make sense if we don't know about the platform