virtio-msg: move compatibility rules in basic concepts

Move version compatibility rules in a sub-chapter of transport revision
in the basic concepts.
This is to prepare for the removal of the compliance chapter.

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

Author: bertrand-marquis

transport-msg.tex

@@ -190,6 +190,15 @@ \subsubsection{Transport Revisions and Maximum Message Size}
 This value is large enough to support a GET_CONFIG or SET_CONFIG message with a
 configuration data payload of 256 bytes.
 
+\paragraph{Versioning and Forward Compatibility}
+
+A higher transport \textbf{transport revision} or additional \textbf{feature
+bits} MAY extend the protocol with new messages or capabilities. However,
+to remain compliant with earlier revisions, devices and drivers SHOULD
+continue to honor the mandatory messages and semantics from prior revisions. If
+a bus instance or device does not support an advanced feature, it SHOULD
+reject or ignore those requests rather than undefined behavior.
+
 \subsubsection{Device Numbers and Enumeration}
 \label{sec:Virtio Transport Options / Virtio Over Messages / Basic Concepts /
 Device Numbers}
@@ -1392,13 +1401,3 @@ \subsubsection{Conformance Statements}
 do not invalidate compliance if omitted, provided all required behaviors are
 still correctly implemented.
 
-\subsubsection{Versioning and Forward Compatibility}
-\label{sec:Virtio Transport Options / Virtio Over Messages / Compliance / Versioning}
-
-A higher transport \textbf{transport revision} or additional \textbf{feature
-bits} MAY extend the protocol with new messages or capabilities. However,
-to remain compliant with earlier revisions, devices and drivers SHOULD
-continue to honor the mandatory messages and semantics from prior revisions. If
-a bus instance or device does not support an advanced feature, it SHOULD
-reject or ignore those requests rather than undefined behavior.
-