Add connection variable to greybus_message_sent.
This will be put to more use by a follow-up up patch.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Tested-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>