Tvheadend

In an attempt to reduce the number of syscalls minisatip performs, I tried to buffer multiple RTSP Chunks (RTSP header 0x24 00 len + RTP header (12 bytes) + 42 * 188 TS packets) and issue just one syscall in minisatip.
Reference commit: https://github.com/catalinii/minisatip/commit/71b93ccea20c8bdf2aa3eaca41da0675c303fb2d
The interesting code is in: process_packets_for_stream.

Basically the only change from the client side is that instead of issuing a writev syscall for 1 RTSP chunk (7912 bytes) now it is possible to issue 1 syscall for the entire for around 72k.

While I thought this will not impact in any way TVH, I see there are some issues and the viewing is completely broken if I call writev for even 2 RTSP chunks. Tried the same test with minisatip as satip client or ffmpeg and both work with no issues.

How to repro with an HD channel:

./minisatip -2 88 -f -l http (does not work)
./minisatip -2 80 -f -l http (works)

The difference is that the second call will call writev after each 42 TS packets, while second will call it after just 1 (same behaviour as before).

The plan is to remove the option completely and call writev only if MAX_IOV is reached (1024)