rtpenc: Simplify code by introducing a macro for rescaling NTP timestamps

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpproto: Support nonblocking reads

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpproto: Remove a misplaced comment

The fdset is a pollfd array nowadays, and it is already populated
at this point.

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpproto: Simplify the rtp_read function by looping over the fds

This avoids having duplicate code where only the fd parameter
differs.

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpproto: Move rtpproto specific function declarations to a separate header

Mixing these with the rtp depacketizer functions in rtpdec.h is
no good.

Signed-off-by: Martin Storsjö <martin@martin.st>