Merge bitcoin/bitcoin#22013: net: ignore block-relay-only peers when skipping DNS seed

fe3d17df04 net: ignore block-relay-only peers when skipping DNS seed (Anthony Towns)

Pull request description:

  Since #17428 bitcoind will attempt to reconnect to two block-relay-only anchors before doing any other outbound connections. When determining whether to use DNS seeds, it will currently see these two peers and decide "we're connected to the p2p network, so no need to lookup DNS" -- but block-relay-only peers don't do address relay, so if your address book is full of invalid addresses (apart from your anchors) this behaviour will prevent you from recovering from that situation.

  This patch changes it so that it only skips use of DNS seeds when there are two full-outbound peers, not just block-relay-only peers.

ACKs for top commit:
  Sjors:
    utACK fe3d17d
  amitiuttarwar:
    ACK fe3d17df04, this impacts the very common case where we stop/start a node, persisting anchors & have a non-empty addrman (although, to be clear, wouldn't be particularly problematic in the common cases where the addrman has valid addresses)
  mzumsande:
    ACK fe3d17df04
  jonatack:
    ACK fe3d17df04
  prayank23:
    tACK fe3d17df04

Tree-SHA512: 9814b0d84321d7f45b5013eb40c420a0dd93bf9430f5ef12dce50d1912a18d5de2070d890a8c6fe737a3329b31059b823bc660b432d5ba21f02881dc1d951e94

src/net.cpp

@@ -1638,7 +1638,7 @@ void CConnman::ThreadDNSAddressSeed()
                     {
                         LOCK(cs_vNodes);
                         for (const CNode* pnode : vNodes) {
-                            if (pnode->fSuccessfullyConnected && pnode->IsOutboundOrBlockRelayConn()) ++nRelevant;
+                            if (pnode->fSuccessfullyConnected && pnode->IsFullOutboundConn()) ++nRelevant;
                         }
                     }
                     if (nRelevant >= 2) {