SM6FBQ / HackRF clone - History

Wait for TX buffer flush at end of hackrf_transfer.

Add API to support flushing the device buffer when TX finishes.

Call TX callback to fill transfers before initial submission.

Use an early return to reduce indentation in prepare_transfers.

Remove message when rewinding input file.

For small input files this may be printed a very large number of times.

In repeat mode, rewind file as many times as needed to fill buffer.

Fixes #720.

Use some early returns to reduce deeply indented callbacks.