NFS: NFSERR_INVAL is not defined by NFSv2

A documenting comment in include/uapi/linux/nfs.h claims incorrectly
that NFSv2 defines NFSERR_INVAL. There is no such definition in either
RFC 1094 or https://pubs.opengroup.org/onlinepubs/9629799/chap7.htm

NFS3ERR_INVAL is introduced in RFC 1813.

NFSD returns NFSERR_INVAL for PROC_GETACL, which has no
specification (yet).

However, nfsd_map_status() maps nfserr_symlink and nfserr_wrong_type
to nfserr_inval, which does not align with RFC 1094. This logic was
introduced only recently by commit 438f81e0e92a ("nfsd: move error
choice for incorrect object types to version-specific code."). Given
that we have no INVAL or SERVERFAULT status in NFSv2, probably the
only choice is NFSERR_IO.

Fixes: 438f81e0e92a ("nfsd: move error choice for incorrect object types to version-specific code.")
Reviewed-by: NeilBrown <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

fs/nfsd/nfs2acl.c

···
 	inode = d_inode(fh->fh_dentry);
 
 	if (argp->mask & ~NFS_ACL_MASK) {
-		resp->status = nfserr_inval;
+		resp->status = nfserr_io;
 		goto out;
 	}
 	resp->mask = argp->mask;

fs/nfsd/nfsproc.c

···
 		break;
 	case nfserr_symlink:
 	case nfserr_wrong_type:
-		status = nfserr_inval;
+		status = nfserr_io;
 		break;
 	}
 	return status;

include/uapi/linux/nfs.h

···
 	NFSERR_NODEV = 19,		/* v2 v3 v4 */
 	NFSERR_NOTDIR = 20,		/* v2 v3 v4 */
 	NFSERR_ISDIR = 21,		/* v2 v3 v4 */
-	NFSERR_INVAL = 22,		/* v2 v3 v4 */
+	NFSERR_INVAL = 22,		/*    v3 v4 */
 	NFSERR_FBIG = 27,		/* v2 v3 v4 */
 	NFSERR_NOSPC = 28,		/* v2 v3 v4 */
 	NFSERR_ROFS = 30,		/* v2 v3 v4 */