nfs42: client needs to strip file mode's suid/sgid bit after ALLOCATE op

The Linux NFS server strips the SUID and SGID from the file mode
on ALLOCATE op.

Modify _nfs42_proc_fallocate to add NFS_INO_REVAL_FORCED to
nfs_set_cache_invalid's argument to force update of the file
mode suid/sgid bit.
Suggested-by: Trond Myklebust <trondmy@hammerspace.com>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs42proc.c

@@ -81,7 +81,8 @@ static int _nfs42_proc_fallocate(struct rpc_message *msg, struct file *filep,
 	if (status == 0) {
 		if (nfs_should_remove_suid(inode)) {
 			spin_lock(&inode->i_lock);
-			nfs_set_cache_invalid(inode, NFS_INO_INVALID_MODE);
+			nfs_set_cache_invalid(inode,
+				NFS_INO_REVAL_FORCED | NFS_INO_INVALID_MODE);
 			spin_unlock(&inode->i_lock);
 		}
 		status = nfs_post_op_update_inode_force_wcc(inode,