ffm options should also set discard automatically.

commit 13f6917c handles discards automatically,
but the ffm discard options are not fully parsed. Causing the input streams not
to be used, so no stream towards the ffserver after the initial probing.

Signed-off-by: Rick van der Zwet <info@rickvanderzwet.nl>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>