bluetooth: windows: Mark characteristic discovered

Currently characteristics are not getting marked discovered.  This
change fixes that.

At the moment, this does not bubble up a services discovered event, so
a test for this will be made in a subsequent change.
https://chromium-review.googlesource.com/c/chromium/src/+/730653/

BUG=507419

Change-Id: Ie6a510ee2ae6d97e34760822fe7b01f65e28337d
Reviewed-on: https://chromium-review.googlesource.com/735983
Commit-Queue: Conley Owens <[email protected]>
Reviewed-by: Vincent Scheib <[email protected]>
Reviewed-by: Matt Reynolds <[email protected]>
Cr-Commit-Position: refs/heads/master@{#517677}
3 files changed