Bug 5497: Fix detection of duped IPs returned by getaddrinfo() (#2100)

Bug 5497: Fix detection of duped IPs returned by getaddrinfo() (#2100)

    WARNING: Ignoring <IP X> because it is already covered by <IP X>

Affects `src`, `dst`, and `localip` ACLs, especially those that use
domain names with multiple DNS A or AAAA records.

IP addresses returned by getaddrinfo(3) may not be sorted (e.g., when a
host has multiple DNS A RRs on FreeBSD). Instead of comparing the
current address with just the previous one, we now check all previously
added addresses (while processing a single getaddrinfo() call output).

This surgical fix minimizes changes without improving surrounding code.