fix a bug in the input sanity check of DIOCCHANGERULE (not used by pfctl,
but third-party tools). a rule must have a non-empty replacement address
list when it's a translation rule but not an anchor call (i.e. "nat ...
->" needs a replacement address, but "nat-anchor ..." doesn't). the check
confused "rule is an anchor call" with "rule is defined within an anchor".
report from Michal Mertl, Max Laier.
Obtained from: OpenBSD
MFC after: 2 weeks