This is essential if a format contains e.g. the number of probes; the
init() function needs to initialize the sr_dev_inst struct, but needs
access to the file to properly add the probes to it.
This is a small helper function which sends the SR_DF_HEADER packet that
drivers usually emit in their hw_dev_acquisition_start() API callback.
It simplifies and shortens the hw_dev_acquisition_start() functions
quite a bit.
It also simplifies the input modules which send an SR_DF_HEADER packet, too.
This patch also automatically removes some unneeded malloc/free in some
drivers for the 'packet' and 'header' structs used for SR_DF_HEADER.
Since input modules determine a samplerate by reading from their
file format (or having it overridden with an option), they need
to pass this up to the frontend.
Uwe Hermann
Martin Ling
Bert Vermeulen
Petteri Aimonen