MFC 208213:

Prevent unloading a kld for a driver that has subinterfaces (vlan and/or
wlan interfaces) from being automatically reloaded via devd shutdown
event handlers.
- Revert part of my previous changes to call ifn_stop on subinterfaces
  when an interface is detached.  It is better to destroy the interfaces
  first so that an 'ifconfig foo0.blah down' doesn't result in ifconfig
  auto-loading if_foo.ko.  The ifconfig command will not be invoked if
  foo0.blah is gone when ifn_stop() is called.  Furthermore, it is not
  necessary to explicitly invoke ifn_stop() after the subinterface is
  destroyed as devd will already do that.
- Pass -n to ifconfig when destroying interfaces so that destroying a
  cloned interface does not kldload any drivers.

etc/network.subr

@@ -516,7 +516,7 @@ clone_down()
 	_prefix=
 	_list=
 	for ifn in ${cloned_interfaces}; do
-		ifconfig ${ifn} destroy
+		ifconfig -n ${ifn} destroy
 		if [ $? -eq 0 ]; then
 			_list="${_list}${_prefix}${ifn}"
 			[ -z "$_prefix" ] && _prefix=' '
@@ -599,10 +599,7 @@ childif_destroy()
 		if ! ifexists $child; then
 			continue
 		fi
-		if autoif $child; then
-			ifn_stop $child
-		fi
-		ifconfig $child destroy && cfg=0
+		ifconfig -n $child destroy && cfg=0
 	done
 
 	child_vlans=`get_if_var $ifn vlans_IF`
@@ -613,10 +610,7 @@ childif_destroy()
 		if ! ifexists $child; then
 			continue
 		fi
-		if autoif $child; then
-			ifn_stop $child
-		fi
-		ifconfig $child destroy && cfg=0
+		ifconfig -n $child destroy && cfg=0
 	done
 
 	return ${cfg}