increase max_video_br due to tivo 9.3a software fix

increase max_video_br due to tivo 9.3a software fix

The 17408k maxrate limit appears to be fixed with pytivo 9.3a in
my tests since receiving the upgrade last week.  I'm increasing
max_video_br so that all known HD bitrates are passed without
transcoding unless the user lowers the setting to force transcoding
of problem files.  Any remaining problems with mpeg transfers
appear to fixable by doing a VideoReDo QuickSteam Fix or similar
mpeg repair.  But I'm not removing maxrate and bufsize options
from the ffmpeg template because my tests show they are still
needed to correct errors in source files which result in playback
problems when these settings are removed.  Increasing maxrate to
30000k does not appear to introduce any playback problems in my
tests of transcodes sent to S2 and S3 tivos.