net: qrtr: Add control packet definition to uapi

The QMUX protocol specification defines structure of the special control
packet messages being sent between handlers of the control port.

Add these to the uapi header, as this structure and the associated types
are shared between the kernel and all userspace handlers of control
messages.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>