resolve: slightly optimize dns_answer_add()

Previously, dns_answer_add() was O(n^2).
With this change dns_packet_extract() becomes ~15 times faster for some
extremal case.

Before:
```
$ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808
/home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok

real    0m15.453s
user    0m15.430s
sys     0m0.007s
```

After:
```
$ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808
/home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok

real    0m0.831s
user    0m0.824s
sys     0m0.006s
```

Hopefully fixes oss-fuzz#19227.
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19227

1 files changed, 1 insertions, 1 deletions

diff --git a/src/resolve/resolved-dns-rr.c b/src/resolve/resolved-dns-rr.c
index c848da3ccb..19e075479f 100644
--- a/src/resolve/resolved-dns-rr.c
+++ b/src/resolve/resolved-dns-rr.c
@@ -1479,7 +1479,7 @@ void dns_resource_record_hash_func(const DnsResourceRecord *rr, struct siphash *
         }
 }
 
-static int dns_resource_record_compare_func(const DnsResourceRecord *x, const DnsResourceRecord *y) {
+int dns_resource_record_compare_func(const DnsResourceRecord *x, const DnsResourceRecord *y) {
         int r;
 
         r = dns_resource_key_compare_func(x->key, y->key);