Switched ai and hi in vorbisenc.c

From l.1089-1148 in lib/vorbisenc.c, the set function set the input argument to the default, and the GET function SET the output (NULL) to the system, i.e. the GET function is actually SET and vice versa. This should be a huge bug.

I made this bug a "major" bug. If this is not the case, just close this ticket.