tests: Bluetooth: ISO: BIS: Add fragmented data test

Add a test for broadcast ISO that uses fragmentation.
The host will attempt to send SDUs 3 times the HCI ISO
data buffer size, so that it will be fragmented into a
BT_ISO_START, BT_ISO_CONT and a BT_ISO_END HCI ISO data
packet.

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