leaudio: Fix attaching device to the stream

This fixes attaching device to the stream in following scenario
1. both devices streaming
2. one device desconnects
3. stream stops and start on a single bud
4. second device reconnectes and does not change any available context
   types

Bug: 319432344
Test: atest bluetooth_le_audio_test
Tag: feature
Flag: Exempt, le audio fix covered with new unit test. Regression tested
with previous unit tests

Change-Id: If33a0f9cbbab01b8a03d60b20242c4e35c529396