In scoring our NHEs during shutdown there is a chance we could release mutliple
NHEs at the same time during one iteration. This can cause memory corruption
if the two being released are directly next to each other in the hash table.
hash_iterate accounts for releasing one during the iteration but not
two by setting hbnext before release but if hbnext is also freed,
we obviously can have a problem.
Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>