policy_is_reject_star():

ome policies are default-reject, some default-accept.  But
policy_is_reject_star() assumed they were all default_reject.  Fix
that!

Also, document that policy_is_reject_star() treats a NULL policy as
empty. This allows us to simplify the checks in
parse_reachable_addresses() by quite a bit.

Fxes bug 20306; bugfix on 0.2.8.2-alpha.