Bluetooth: Queue diagnostic messages together with HCI packets

Sending diagnostic messages directly to the monitor socket might cause
issues for devices processing their messages in interrupt context. So
instead of trying to directly forward them, queue them up with the other
HCI packets and lets them be processed by the sockets at the same time.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>