Bluetooth: BAP: Fix missing cfg data in stream->codec_cfg for BIS

The codec configuration data from the BIS in the BASE was not
properly copied to the stream->codec_cfg, and thus it only
contained the subgroup codec configuration values.

This commit fixes that by first copying the subgroup codec
configuration to the stream, and then setting or overwriting
any fields (if they exist).

This requires that each stream have their own codec configuration
struct allocated, so this will slightly increase memory usage.

This also adds verification of the SDU size from the BIGInfo
in the ISO receive callback.

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