MFC r248674:

MFC r248674:
Make g_wither_washer() to not loop by itself, but only when there was some
more topology change done that may require its attention.  Add few missing
g_do_wither() calls in respective places to signal it.

This fixes potential infinite loop here when some provider is withered, but
still opened or connected for some reason and so can not be destroyed.  For
example, see r227009 and r227510.

git-svn-id: svn://svn.freebsd.org/base/stable/9@249619 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f