dvdplayer: complete the update of ffmpeg interrupt interface

The old interface could not handle being called from another thread
udp: Fix sign of error codes.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
udp: fix non-blocking and interrupt handling.

In non-blocking mode, lowest-level read protocols are
supposed block only for a short amount of time to let
retry_transfer_wrapper() check for interrupts.

Also, checking the interrupt_callback in the receiving thread is
wrong, as interrupt_callback is not guaranteed to be thread-safe
and the job is already done by retry_transfer_wrapper(). The error
code was also incorrect.

Bug reported by Andrey Utkin.
dvdplayer: make sure member variables are inited in constructor
dvdplayer: make sure we can also abort the open of a ffmpeg input stream
Merge pull request #2557 from elupus/abort

dvdplayer: fix abort of ffmpeg streams