Bluetooth: BAP: Fix issue with setting invalid iso data path

BAP would always set up the ISO data path in both directions,
even for unidirectional CIS. This meant that in the
unconfigured direction, the data path configuration data
would all be 0, which causes issues on some controllers.

The new refactored approach implemented by this commit
will always ensure that the data path is setup correctly,
and that we only set the data path in one direction for
unidirectional CIS. The unset path will use the default
ISO path of HCI and transparant format, which should always
be allowed by a controller.

This is building on the requirement in BAP that all streams in
a unicast group shall be QoS configured at the same time. This
ensures that before any streams in the CIG has been connected,
they have all been configured.

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