MFC 201196:

MFC 201196:
Change vlan interfaces to cope more usefully with the parent interface being
renamed.  Previously the vlan interfaces would lose their configuration as if
the parent interface had been physically removed.  Now vlan interfaces ignore
rename events.
- Add a new ifnet flag (IFF_RENAMING) that is set while an ifnet is being
  renamed.  This flag can be checked in ifnet departure/arrival event
  handlers to treat rename events differently.
- Change the ifnet departure event handler in the if_vlan(4) driver to
  ignore departure events due to a trunk interface being renamed.

git-svn-id: svn://svn.freebsd.org/base/stable/8@201597 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f