leaudio: Make sure to do service operations on encrypted link

If GATT reported service disconvery completed when link is not
encrypted, LeAudio profiles should not to start any operations.

Bug: 290879124
Test: atest bluetooth_le_audio_client_test bluetooth_vc_test
bluetooth_has_test bluetooth_csis_test
Tag: #feature

Change-Id: I0981f8bc46a518de6bebd7ae484c0437bf8dee13