Merge bitcoin#29850: net: Decrease nMaxIPs when learning from DNS seeds

f2e3662 net: Decrease nMaxIPs when learning from DNS seeds (laanwj)

Pull request description:

  Limit number of IPs learned from a single DNS seed to 32, to prevent the results from one DNS seed from dominating AddrMan. Note that the number of results from a UDP DNS query is bounded to 33 already, but it is possible for it to use TCP where a larger number of results can be returned.

  Closes bitcoin#16070.

ACKs for top commit:
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    utACK f2e3662
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    ACK f2e3662
  1440000bytes:
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  mzumsande:
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Tree-SHA512: 3f108c2baba7adfedb8019daaf60aa00e628b38d3942e1319c7183a4683670be01929ced9e6372c8e983c902e8633f81fbef12d7cdcaadd7f77ed729c1019942

src/net.cpp

@@ -2256,7 +2256,11 @@ void CConnman::ThreadDNSAddressSeed()
             if (!resolveSource.SetInternal(host)) {
                 continue;
             }
-            unsigned int nMaxIPs = 256; // Limits number of IPs learned from a DNS seed
+            // Limit number of IPs learned from a single DNS seed. This limit exists to prevent the results from
+            // one DNS seed from dominating AddrMan. Note that the number of results from a UDP DNS query is
+            // bounded to 33 already, but it is possible for it to use TCP where a larger number of results can be
+            // returned.
+            unsigned int nMaxIPs = 32;
             const auto addresses{LookupHost(host, nMaxIPs, true)};
             if (!addresses.empty()) {
                 for (const CNetAddr& ip : addresses) {