Bring some improvment to h3_parse_settings_frm() function. The first one is the parsing which now manipulates a buffer instead of a plain char*. This is more to unify with other parsing functions rather than dealing with data wrapping : it's unlikely to happen as SETTINGS is only received as the first frame on the control STREAM. Various errors are now properly reported as connection error : * on incomplete frame payload * on a duplicated settings in the same frame * on reserved settings receive