MFC r206469:

MFC r206469:

  In if_detach_internal() only try to do the detach run if if_attachdomain1()
  has actually succeeded to initialize and attach.  There is a theoretical
  possibility to drop out early in if_attachdomain1() leaving the array
  uninitialized if we cannot get the lock.

  Discussed with:       rwatson

git-svn-id: svn://svn.freebsd.org/base/stable/8@207011 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f