nfs: add new tracepoint at nfs4 revalidate entry point

Add a call to the v4 d_revalidate entrypoint, just like the v3 one.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/dir.c

@@ -2194,6 +2194,8 @@ nfs4_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 {
 	struct inode *inode;
 
+	trace_nfs_lookup_revalidate_enter(dir, dentry, flags);
+
 	if (!(flags & LOOKUP_OPEN) || (flags & LOOKUP_DIRECTORY))
 		goto full_reval;
 	if (d_mountpoint(dentry))