ff_network_wait_fd_timeout: do not break with timeout < 0

Most code treats timeout < 0 like 0 already

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
tcp: Use a default timeout of 5 sec for opening a connection but not for receiving packets

This should be closer to how tcp behaved longer ago and should
fix the issue with idle connections timing out.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>