Bluetooth: ISO: Add bitmask for retrieving iso header lenght

Add a macro to retrieve the iso data load length (the
length stored in the iso header) with a bit mask that
ensures that we only take the first 14 bits.

This is to remove any RFU bits that may have been set.

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