Move enabling the policy refcounting from policy_ref() to config_free_policy().

Move enabling the policy refcounting from policy_ref() to config_free_policy().
In config_free_policy() the refcounting is unchanged and each SA linked to the
policy will trigger a call to policy_ref() and increase the references as
before the change.  This allows unconditional calls to policy_ref() and
policy_unref() and the callers no longer have to check if IKED_POLICY_REFCNT
is set.

From and ok markus@