PR/56496: Hauke Fath: etcupdate(8) merge formatting issue

Follow suit and turn off OXTABS by default

FreeBSD did that in 1994:

r3505 | wollman | 1994-10-10 20:16:28 -0400 (Mon, 10 Oct 1994) | 5 lines
    Turn off OXTABS by default.  Inspection of systems here finds no commercial
    systems with it on by default (or the equivalent flag) and terminal control
    sequences confuse it greatly.  (Try running `ls' under bash in an XTerm,
    for instance.)

OpenBSD did that in 2019:

date: 2019/03/12 11:01:25;  author: nicm;  state: Exp;  lines: +2 -2;
commitid: XOmQAZHjspUKWzDx;
    Almost all terminals now support hardware tabs so default to OXTABS off.

    This makes three changes: adds the ht capability to the standard lines
    in gettytab(5); removes OXTABS from TTYDEF_OFLAG in ttydefaults.h (the
    defaults used by pty(4) - diff from martijn); and only sets OXTABS on
    terminals which lack hts and tbc in tset(1) (from Thomas Dickey
    upstream).

    Addresses problems reported by tedu.

    ok millert

sys/sys/ttydefaults.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: ttydefaults.h,v 1.16 2008/05/24 14:06:39 yamt Exp $	*/
+/*	$NetBSD: ttydefaults.h,v 1.17 2021/11/20 14:52:22 christos Exp $	*/
 
 /*-
  * Copyright (c) 1982, 1986, 1993
@@ -46,7 +46,7 @@
  * Defaults on "first" open.
  */
 #define	TTYDEF_IFLAG	(BRKINT | ICRNL | IMAXBEL | IXON | IXANY)
-#define TTYDEF_OFLAG	(OPOST | ONLCR | OXTABS)
+#define TTYDEF_OFLAG	(OPOST | ONLCR)
 #define TTYDEF_LFLAG	(ECHO | ICANON | ISIG | IEXTEN | ECHOE|ECHOKE|ECHOCTL)
 #define TTYDEF_CFLAG	(CREAD | CS8 | HUPCL)
 #define TTYDEF_SPEED	(B9600)