Do not treat backslashe as an escape character in hostname.if(5) lines

ifstart() should always pass such lines unaltered, especially if they
contain "nwid" or "description" lines with arbitrary strings.
<bsdlisten at gmail dot com> reported SSIDs such as "Mike's" during
installation end as broken;  this was because the installer escaped
the single quote using backslashes which ended up being treated as
escape characters much later during hostname.if parsing in netstart(8).
Ok deraadt

src/etc/netstart

@@ -1,6 +1,6 @@
 #!/bin/sh -
 #
-#	$OpenBSD: netstart,v 1.202 2020/01/15 00:19:40 kn Exp $
+#	$OpenBSD: netstart,v 1.203 2020/05/21 11:54:41 kn Exp $
 
 # Turn off Strict Bourne shell mode.
 set +o sh
@@ -134,7 +134,7 @@ ifstart() {
 	# Parse the hostname.if(5) file and fill _cmds array with interface
 	# configuration commands.
 	set -o noglob
-	while IFS= read -- _line; do
+	while IFS= read -r -- _line; do
 		parse_hn_line $_line
 	done <$_hn