MFC 208213:

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.

git-svn-id: svn://svn.freebsd.org/base/stable/8@208384 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f