virtio-msg normative in bus vs transport relationship

Add bus normative statement in bus vs transport section of basic
concepts.

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>

Author: bertrand-marquis

transport-msg.tex

@@ -108,13 +108,18 @@ \subsubsection{Relationship Between Bus and Transport}
       \item Handling device status and notifications (\msgref{SET_DEVICE_STATUS},
         \msgref{EVENT_USED}, etc.).
     \end{itemize}
-    A bus implementation MUST relay these messages to the device number
-    identified in the header, regardless of how it discovered or enumerated
-    that device. Apart from enforcing generic transport limits (for example,
-    maximum message size), a bus SHOULD treat transport messages as opaque and
-    avoid modifying them.
 \end{description}
 
+\busnormative{\paragraph}{Transport Message Forwarding}{Virtio Transport Options / Virtio Over Messages / Basic Concepts / Relationship between bus and transport / Transport Message Forwarding}
+\begin{itemize}
+  \item A bus implementation MUST relay each transport message to the device
+        number identified in the message header, regardless of how it
+        discovered or enumerated that device.
+  \item A bus implementation SHOULD treat transport messages as opaque apart
+        from enforcing generic transport limits, such as the advertised maximum
+        message size, and SHOULD NOT modify the transport payload.
+\end{itemize}
+
 This separation lets a bus remain minimal if it obtains device information from
 firmware tables, while still supporting fully message-based enumeration and
 hotplug when desired.
@@ -1400,4 +1405,3 @@ \subsubsection{Conformance Statements}
 themselves conformant. Features or messages labeled as "optional" (MAY)
 do not invalidate compliance if omitted, provided all required behaviors are
 still correctly implemented.
-