public/gnttab: relax v2 recommendation

With there being a way to disable v2 support, telling new guests to use
v2 exclusively is not a good suggestion.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>

xen/include/public/grant_table.h

@@ -121,8 +121,9 @@ typedef uint32_t grant_ref_t;
  */
 
 /*
- * Version 1 of the grant table entry structure is maintained purely
- * for backwards compatibility.  New guests should use version 2.
+ * Version 1 of the grant table entry structure is maintained largely for
+ * backwards compatibility.  New guests are recommended to support using
+ * version 2 to overcome version 1 limitations, but to default to version 1.
  */
 #if __XEN_INTERFACE_VERSION__ < 0x0003020a
 #define grant_entry_v1 grant_entry