This allows the user to explicitly select the behaviour of the write to the
remote peripheral. This is needed for peripherals that have
characteristics with WRITE_NO_RESPONSE set (instead of normal WRITE). The
function's signature is now:
BLE.gattc_write(conn_handle, value_handle, data, mode=0)
mode=0 means write without response, while mode=1 means write with
response. The latter was the original behaviour so this commit is a change
in behaviour of this method, and one should specify 1 as the 4th argument
to get back the old behaviour.
In the future there could be more modes supported, such as long writes.