Remove reference to btcontrol(8) and clarify mixer(4)

usr.bin/bthset/bthset.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: bthset.1,v 1.3 2006/07/30 00:03:22 wiz Exp $
+.\"	$NetBSD: bthset.1,v 1.4 2006/08/19 16:37:26 plunky Exp $
 .\"
 .\" Copyright (c) 2006 Itronix Inc.
 .\" All rights reserved.
@@ -48,7 +48,9 @@ The
 utility is used to access a Bluetooth Headset with the
 .Xr btsco 4
 audio device.
-It opens the mixer device and creates the control connection
+It opens the
+.Xr mixer 4
+device and creates the control connection
 to the headset, then conducts volume settings each way.
 When
 .Nm
@@ -109,7 +111,7 @@ Be verbose.
 .Pa /dev/mixer
 .Sh SEE ALSO
 .Xr btsco 4 ,
-.Xr btcontrol 8
+.Xr mixer 4
 .Sh AUTHORS
 .An Iain Hibbert
 for Itronix, Inc