MFC 209178

MFC 209178
 * Fix a bug where the length of the ASCONF-ACK was calculated wrong due
   to using an uninitialized variable.
 * Fix a bug where a NULL pointer was dereferenced when interfaces
   come and go at a high rate.
 * Fix a bug where inps where not deregistered from iterators.
 * Fix a race condition in freeing an association.
 * Fix a refcount problem related to the iterator.
 Each of the above bug results in a panic. It shows up when
 interfaces come and go at a high rate.

git-svn-id: svn://svn.freebsd.org/base/stable/8@209264 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f