LeAudio: Improve handling codec frame blocks other than 1

The number of codec frame blocks per SDU has an impact on
the SDU size and the data interval. The new unit tests
make sure this is taken into the account.

Note: Codec frame blocks per SDU parameter can be other than 1 only with
the codec extensibility feature enabled.

Bug: 313054645
Bug: 308428644
Test: atest bluetooth_le_audio_client_test bluetooth_le_audio_test
Change-Id: I9ddf057548f6ea7952d3bbdfa76dd8e75adeeefb