stream-manager: Improve sending ducking state changed signal

stream-manager: Improve sending ducking state changed signal

If two or more ducking requests have been activated to the same
target stream type during ducking operation, ducking state changed
signal should be emitted for each ducking request handle respectively.
Previously, it did not work well. It is now fixed.

Note that these ducking state changed signals will be emitted at the
same time when the sink-input's ramp finish hook is called in the
thread context as soon as the final ducking operation has been done.

[Version] 11.1.97
[Issue Type] Bug fix

Change-Id: I3de608a7053c6c61e74ff67af271d2972f5149a1
Signed-off-by: Sangchul Lee <sc11.lee@samsung.com>