tests: Bluetooth: Audio: Use same recv_cb for all tests

This commit changes the BSIM tests to use the same recv callback
for all tests. The purpose of this is to reduce code duplication
and make it easier to maintain the tests.

This also changes the recv_cb so that in case of any error we log
the most recently received SDU, which should provide more
information about why a test failed in case of RX error.

PBP had to be updated a bit to support the audio_stream
struct.

Also modifies a check and log in bap_stream that was less than
helpful to determine if it was the stream or the endpoint that
was NULL.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>