Fix a bug introduced with r251190, in which a small hunk was forgotten in

the performance conversion process.

The effect of this was the following error when selecting the menu
"Startup"->"View/Edit Startup Configuration"->"Add New"->"Add From List":

[: -eq: unexpected operator

By running `bsdconfig -d' as root to enable debugging, this turns into:

DEBUG: f_getvar: var=[text] value=[
Error: Expected a number for token 4 of --menu.
Use --help to list options.] r=0
[: -eq: unexpected operator

Indicating that the fourth token for --menu which should be $height was
instead a string (the first item of $menu_list) because it was using the
old size-calculation method and $size was now null (needed to use instead
the new size variables of $height $width and $rows).

usr.sbin/bsdconfig/startup/share/rcconf.subr

@@ -437,7 +437,8 @@ f_dialog_input_rclist()
 		--ok-label \"\$msg_ok\"            \
 		--cancel-label \"\$msg_cancel\"    \
 		${SHOW_DESC:+--item-help}          \
-		--menu \"\$prompt\" $size          \
+		--menu \"\$prompt\"                \
+		$height $width $rows               \
 		$menu_list                         \
 		2>&1 >&$DIALOG_TERMINAL_PASSTHRU_FD
 	)