Incorrect libcap_net limitation list manipulation

In versions of FreeBSD 13-RELEASE before 13-RELEASE-p5, under certain circumstances the cap_net libcasper(3) service incorrectly validates that updated constraints are strictly subsets of the active constraints.  When only a list of resolvable domain names was specified without setting any other limitations, an application could submit a new list of domains including include entries not previously listed.  This could permit the application to resolve domain names that were previously restricted.