Avoid test-before-evict evictions of current peers

Outbound peer logic prevents connecting to addresses that we're already
connected to, so prevent inadvertent eviction of current peers via
test-before-evict by checking this condition and marking current peer's
addresses as Good().

Co-authored-by: John Newbery <john@johnnewbery.com>

src/net.cpp

@@ -1999,11 +1999,30 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
             if (nTries > 100)
                 break;
 
-            CAddrInfo addr = addrman.SelectTriedCollision();
+            CAddrInfo addr;
 
-            // SelectTriedCollision returns an invalid address if it is empty.
-            if (!fFeeler || !addr.IsValid()) {
-                addr = addrman.Select(fFeeler);
+            if (fFeeler) {
+                // First, try to get a tried table collision address. This returns
+                // an empty (invalid) address if there are no collisions to try.
+                addr = addrman.SelectTriedCollision();
+
+                if (!addr.IsValid()) {
+                    // No tried table collisions. Select a new table address
+                    // for our feeler.
+                    addr = addrman.Select(true);
+                } else if (AlreadyConnectedToAddress(addr)) {
+                    // If test-before-evict logic would have us connect to a
+                    // peer that we're already connected to, just mark that
+                    // address as Good(). We won't be able to initiate the
+                    // connection anyway, so this avoids inadvertently evicting
+                    // a currently-connected peer.
+                    addrman.Good(addr);
+                    // Select a new table address for our feeler instead.
+                    addr = addrman.Select(true);
+                }
+            } else {
+                // Not a feeler
+                addr = addrman.Select();
             }
 
             // Require outbound connections, other than feelers, to be to distinct network groups