Bluetooth: Add support for L2CAP 'Send RRorRNR' action

When called, 'Send RRorRNR' should send a RNR frame if local device is
busy or a RR frame otherwise.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>