Merge bitcoin/bitcoin#32073: net: Block v2->v1 transport downgrade if !fNetworkActive

6869fb4 net: Block v2->v1 transport downgrade if !CConnman::fNetworkActive (Hodlinator)

Pull request description:

  We might have just set `CNode::fDisconnect` in the first loop because of `!CConnman::fNetworkActive`.

  Attempting to reconnect using v1 transport just because `fNetworkActive` was set to `false` at the "right" stage in the v2 handshake does not make sense.

  Issue [discovered](bitcoin/bitcoin#31633 (comment)) by davidgumberg.

ACKs for top commit:
  davidgumberg:
    Tested and Reviewed ACK 6869fb4
  mabu44:
    ACK 6869fb4
  stratospher:
    ACK 6869fb4. I've reviewed the code but don't have strong preference for this branch vs master since only functional change is just a single log not being printed in a low probability scenario (we happen to be attempting v2 connection when P2P network activity is being turned off).
  vasild:
    ACK 6869fb4

Tree-SHA512: 54f596e54c5a6546f2c3fec2609aa8d10dec3adcf1001ca16666d8b374b8d79d64397f46c90d9b3915b4e91a5041b6ced3044fd2a5b4fb4aa7282eb51f61296a

Author: ryanofsky

src/net.cpp

@@ -1912,7 +1912,8 @@ void CConnman::DisconnectNodes()
     {
         LOCK(m_nodes_mutex);
 
-        if (!fNetworkActive) {
+        const bool network_active{fNetworkActive};
+        if (!network_active) {
             // Disconnect any connected nodes
             for (CNode* pnode : m_nodes) {
                 if (!pnode->fDisconnect) {
@@ -1934,7 +1935,7 @@ void CConnman::DisconnectNodes()
                 // Add to reconnection list if appropriate. We don't reconnect right here, because
                 // the creation of a connection is a blocking operation (up to several seconds),
                 // and we don't want to hold up the socket handler thread for that long.
-                if (pnode->m_transport->ShouldReconnectV1()) {
+                if (network_active && pnode->m_transport->ShouldReconnectV1()) {
                     reconnections_to_add.push_back({
                         .addr_connect = pnode->addr,
                         .grant = std::move(pnode->grantOutbound),