net: manually resolve dns seed sources

Note: Some seeds aren't actually returning an IP for their name entries, so
they're being added to addrman with a source of [::].

This commit shouldn't change that behavior, for better or worse.

src/net.cpp

@@ -1454,7 +1454,15 @@ void ThreadDNSAddressSeed()
                     found++;
                 }
             }
-            addrman.Add(vAdd, CNetAddr(seed.name, true));
+            // TODO: The seed name resolve may fail, yielding an IP of [::], which results in
+            // addrman assigning the same source to results from different seeds.
+            // This should switch to a hard-coded stable dummy IP for each seed name, so that the
+            // resolve is not required at all.
+            if (!vIPs.empty()) {
+                CService seedSource;
+                Lookup(seed.name.c_str(), seedSource, 0, true);
+                addrman.Add(vAdd, seedSource);
+            }
         }
     }