Revert "Stop panicking when fail_with is called twice on a connection"

But keep the extra error information.

zebra-network/src/peer/connection.rs

@@ -525,31 +525,20 @@ where
             .lock()
             .expect("mutex should be unpoisoned");
         if let Some(original_error) = guard.clone() {
-            // A failed connection might experience further errors if we:
-            // 1. concurrently process two different messages
-            // 2. check for a failed state for the second message
-            // 3. fail the connection due to the first message
-            // 4. fail the connection due to the second message
-            //
-            // It's not clear:
-            // * if this is actually a bug,
-            // * how we can modify Zebra to avoid it.
-            //
-            // This warning can also happen due to these bugs:
+            // This panic typically happens due to these bugs:
             // * we mark a connection as failed without using fail_with
             // * we call fail_with without checking for a failed connection
             //   state
             //
-            // See the original bug #1510, the initial fix #1531, and the later
-            // bug #1599.
-            warn!(?original_error,
-                  new_error = ?e,
-                  connection_state = ?self.state,
-                  client_receiver = ?self.client_rx,
-                  "calling fail_with on already-failed connection state: ignoring new error");
-            // we don't need to clean up the connection, the original call to
-            // fail_with does that
-            return;
+            // See the original bug #1510 and PR #1531, and the later bug #1599
+            // and PR #1600.
+            panic!(
+                "calling fail_with on already-failed connection state: failed connections must stop processing pending requests and responses, then close the connection. state: {:?} original error: {:?} new error: {:?} client receiver: {:?}",
+                self.state,
+                original_error,
+                e,
+                self.client_rx
+            );
         } else {
             *guard = Some(e);
         }