gr-soapy: deactivate stream before closing

[willcode]

Pull Request Details

It was reported that, with the HackRF module, a flowgraph terminated
with a segfault. Most Soapy modules implement deactivateStream(), but
that function is not called from gr-soapy.

Problem reported by Gavin Jacobs on the mailing list.

Which blocks/areas does this affect?

gr-soapy

Checklist

• I have read the CONTRIBUTING document.
• I have squashed my commits to have one significant change per commit.
• I have signed my commits before making this PR
• My code follows the code style of this project. See GREP1.md.
• I have updated the documentation where necessary.
• I have added tests to cover my changes, and all previous tests pass.

[willcode]

This needs some testing with various SDR modules before merge. The RTLSDR module calls deactivateStream() from closeStream(). Most other modules look like they expect us to call deactivateStream().

[willcode]

Tested with RTLSDR, HackRF and AirspyHF. The HackRF segv (return code -11) goes away with this patch. The other SDRs did not show any different behavior (which is good). So, I think this is safe and correct.

[willcode]

@ncorgan Could you take a look at this? Thanks.

[ncorgan]

Looks good to me.