afs_conn: make release_conns_vector() actually work

afs_conn: make release_conns_vector() actually work

release_conns_vector must never have been called before with
a non-null parameter, because it could not possibly work.
The first line of the loop is a null pointer dereference, and
if that were fixed, there's also a modify-after-free bug as well.
It's not clear how what the old version was trying to do; this
version makes a stab at doing something sensible but might be
less than required.  (Note that this would be much simpler if
converted to queue(3) macros or a similar standard linked-list
data structure.)

Change-Id: I4c0fb7ed1ee977dcc0b4dfb32557882679069731
Reviewed-on: http://gerrit.openafs.org/7838
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>