Bluetooth: ISO: Don't reject BT_ISO_QOS if parameters are unset

Consider certain values (0x00) as unset and load proper default if
an application has not set them properly.

Fixes: 0fe8c8d0 ("Bluetooth: Split bt_iso_qos into dedicated structures")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>