NFS: Clean-up: Define macros for maximum host and export path name lengths

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_mount.h b/include/linux/nfs_mount.h
index cc8b9c5..0b82a17 100644
--- a/include/linux/nfs_mount.h
+++ b/include/linux/nfs_mount.h
@@ -37,7 +37,7 @@
 	int		acdirmin;		/* 1 */
 	int		acdirmax;		/* 1 */
 	struct sockaddr_in addr;		/* 1 */
-	char		hostname[256];		/* 1 */
+	char		hostname[NFS_MAXNAMLEN + 1];		/* 1 */
 	int		namlen;			/* 2 */
 	unsigned int	bsize;			/* 3 */
 	struct nfs3_fh	root;			/* 4 */