nfsd: include linux/nfs4.h in export.h

export.h refers to the pnfs_layouttype enum, which is defined there.
Signed-off-by: NJeff Layton <jeff.layton@primarydata.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/export.h

@@ -6,6 +6,7 @@
 
 #include <linux/sunrpc/cache.h>
 #include <uapi/linux/nfsd/export.h>
+#include <linux/nfs4.h>
 
 struct knfsd_fh;
 struct svc_fh;