leaudio: Improve handling OnAudioSink/SourceResume

This patch improves handling resuming sink and source when the other one
is in IDLE state

Bug: 150670922
Test: atest --host  bluetooth_le_audio_client_test bluetooth_le_audio_test
Tag: #feature
sponsor: jpawlowski@
Change-Id: I2f0b88d44cdab9cde1744e72cdf3eb27975dbdb0