Suppress noisy intent when a fallback device exist (LE)

This CL suppress noisy intent when both of conditions met:
 - Currently active LE audio device is disconnected.
 - There is a fallback device.

The music will keep playing in this case.

Bug: 275433406
Test: 1) atest ActiveDeviceManagerTest LeAudioBinderTest \
               LeAudioServiceTest MediaControlGattServiceTest \
	       TbsGenericTest;
      2) Manually tested disconnecting active LE headset while another
         A2DP headset is connected. Music kept playing via
         the remaining BT device.
      3) Manually tested selecting phone speaker while playing music
         through LE headset. Music kept playing.
Change-Id: Ibde4cc97ec34c0d5ddf3a06f6486234f3f7a92d0