nfsd: enable V4ROOT exports

With the v4root option now enforced everywhere it should be, it is safe
to advertise support for it to mountd.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

include/linux/nfsd/export.h

@@ -50,7 +50,7 @@
  */
 #define	NFSEXP_V4ROOT		0x10000
 /* All flags that we claim to support.  (Note we don't support NOACL.) */
-#define NFSEXP_ALLFLAGS		0x7E3F
+#define NFSEXP_ALLFLAGS		0x17E3F
 
 /* The flags that may vary depending on security flavor: */
 #define NFSEXP_SECINFO_FLAGS	(NFSEXP_READONLY | NFSEXP_ROOTSQUASH \