refactor, doc: Improve SetupAddressRelay call in version processing

This code was a bit hard to understand, so make it less dense and
add more explanations. Doesn't change behavior.

Co-authored-by: Amiti Uttarwar <amiti@uttarwar.org>

Author: mzumsande

src/net_processing.cpp

@@ -3274,13 +3274,17 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             m_num_preferred_download_peers += state->fPreferredDownload;
         }
 
-        if (!pfrom.IsInboundConn() && SetupAddressRelay(pfrom, *peer)) {
-            // For outbound peers, we do a one-time address fetch
-            // (to help populate/update our addrman).
+        // Attempt to initialize address relay for outbound peers and use result
+        // to decide whether to send GETADDR, so that we don't send it to
+        // inbound or outbound block-relay-only peers.
+        bool send_getaddr{false};
+        if (!pfrom.IsInboundConn()) {
+            send_getaddr = SetupAddressRelay(pfrom, *peer);
+        }
+        if (send_getaddr) {
+            // Do a one-time address fetch to help populate/update our addrman.
             // If we're starting up for the first time, our addrman may be pretty
-            // empty and no one will know who we are, so this mechanism is
-            // important to help us connect to the network.
-            //
+            // empty, so this mechanism is important to help us connect to the network.
             // We skip this for block-relay-only peers. We want to avoid
             // potentially leaking addr information and we do not want to
             // indicate to the peer that we will participate in addr relay.
@@ -5214,8 +5218,9 @@ bool PeerManagerImpl::SetupAddressRelay(const CNode& node, Peer& peer)
     if (node.IsBlockOnlyConn()) return false;
 
     if (!peer.m_addr_relay_enabled.exchange(true)) {
-        // First addr message we have received from the peer, initialize
-        // m_addr_known
+        // During version message processing (non-block-relay-only outbound peers)
+        // or on first addr-related message we have received (inbound peers), initialize
+        // m_addr_known.
         peer.m_addr_known = std::make_unique<CRollingBloomFilter>(5000, 0.001);
     }