Rework hardware probing and RTL-SDR helper startup

The lazy startup of the separate helper program for the RTL-SDR
backend on playback start was incorrect with respect to the expected
behavior the frequency setting verbs.  This was not visible during
usage by the radio application, but was triggering failures in
several tests in the pyagl binding wrapper test suite.  To facilitate
starting the helper during backend initialization, the probing part
of the backend "init" has been split into a separate "probe" function,
and all backends have been updated to reflect this change.  Logic has
been added to enforce that "init" is only called after "probe" has
succeeded for a backend, and a comment has been added to radio_impl.h
to document this intended behavior.

Bug-AGL: SPEC-3717

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ic37331a92bae7cc01ee448e69894fa5f49d08a74

0 files changed, 0 insertions, 0 deletions