Bluetooth: ISO: extend API for setting SDU interval

The BT Core Spec v5.4 allows separate SDU_Interval to
be set on C_To_P and P_To_C directions,
but this is not possible with the existing interface.

This PR splits the interval parameter in the call to
bt_iso_sig_create into one for C_To_P
and one for P_To_C

It also splits the latency parameter into one for
C_To_P and one for P_To_C

Signed-off-by: Andries Kruithof <andries.kruithof@nordicsemi.no>

Bluetooth: ISO: update UI for extended API

The API for setting the SDU interval and latency have been updated.
This PR also updates the setting of these by the user in the shell
and the iso_connected_benchmark sample

Signed-off-by: Andries Kruithof <andries.kruithof@nordicsemi.no>