lpd: require data file path name to be in the spool dir

When processing the control file, any file to be printed must be
located in the spool directory (e.g. dfA000foobar) either as a
regular file or a symbolic link to another file to be printed.  This
matches the handling of the 'U' (unlink) directive.

OK deraadt@

usr.sbin/lpr/lpd/printjob.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: printjob.c,v 1.62 2021/10/24 21:24:18 deraadt Exp $	*/
+/*	$OpenBSD: printjob.c,v 1.63 2026/06/09 21:46:48 millert Exp $	*/
 /*	$NetBSD: printjob.c,v 1.31 2002/01/21 14:42:30 wiz Exp $	*/
 
 /*
@@ -467,6 +467,8 @@ printit(char *file)
 			continue;
 
 		default:	/* some file to print */
+			if (strchr(line+1, '/'))
+				continue;
 			switch (i = print(line[0], line+1)) {
 			case ERROR:
 				if (bombed == OK)