Bluetooth: ISO: Add check for maximum ISO SDU size

Verify that the HCI ISO data packet is smaller than
the maximum SDU size we support, based on the group
settings.

Since we do not yet support fragmentation we also
verify that the data length is smaller than the
HCI ISO buffer size.

For the ISO peripheral is it not possible to know
the SDU, and we are forced to not send any value larger
than the PDU size.

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