Orangefs: define a minimum compatible userspace version.

Signed-off-by: Mike Marshall <hubcap@omnibond.com>

fs/orangefs/protocol.h

@@ -399,6 +399,7 @@ enum {
  * space. Zero signifies the upstream version of the kernel module.
  */
 #define ORANGEFS_KERNEL_PROTO_VERSION 0
+#define ORANGEFS_MINIMUM_USERSPACE_VERSION 20904
 
 /*
  * describes memory regions to map in the ORANGEFS_DEV_MAP ioctl.