Count multiprotocol prefixes in the UPDATE log lines

The 'Sending UPDATE' and 'Received UPDATE' lines counted only the IPv4
fields of the message body, so every IPv6 UPDATE logged announced=0.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/server/src/fsm.rs

@@ -260,12 +260,8 @@ async fn established_loop(
                     }
                     Message::Update(update) => {
                         hold_timer.as_mut().reset(Instant::now() + hold_duration);
-                        info!(
-                            peer = %peer_id,
-                            withdrawn = update.withdrawn_routes.len(),
-                            announced = update.announced_routes.len(),
-                            "Received UPDATE",
-                        );
+                        let (withdrawn, announced) = prefix_counts(&update);
+                        info!(peer = %peer_id, withdrawn, announced, "Received UPDATE");
                         apply_update(adj_rib_in, peer_id, &update.path_attributes,
                             &update.withdrawn_routes, &update.announced_routes).await;
                     }
@@ -286,12 +282,8 @@ async fn established_loop(
             }
             Some(msg) = outbound.recv() => {
                 if let Message::Update(update) = &msg {
-                    info!(
-                        peer = %peer_id,
-                        withdrawn = update.withdrawn_routes.len(),
-                        announced = update.announced_routes.len(),
-                        "Sending UPDATE",
-                    );
+                    let (withdrawn, announced) = prefix_counts(update);
+                    info!(peer = %peer_id, withdrawn, announced, "Sending UPDATE");
                 }
                 send_message(writer, &msg, ctx).await?;
                 // A NOTIFICATION from our side ends the session (RFC 4271 §6).
@@ -390,6 +382,21 @@ async fn close_for_collision(
 // RIB helpers
 // ---------------------------------------------------------------------------
 
+/// Prefixes withdrawn and announced by an UPDATE, across the IPv4 fields in
+/// the message body and the multiprotocol attributes (where IPv6 travels).
+fn prefix_counts(update: &bgp_packet::message::UpdateMessage) -> (usize, usize) {
+    let mut withdrawn = update.withdrawn_routes.len();
+    let mut announced = update.announced_routes.len();
+    for attr in &update.path_attributes {
+        match attr {
+            PathAttribute::MpReachNlri(mp) => announced += mp.prefixes.len(),
+            PathAttribute::MpUnreachNlri(mp) => withdrawn += mp.prefixes.len(),
+            _ => {}
+        }
+    }
+    (withdrawn, announced)
+}
+
 /// Applies a received UPDATE to the Adj-RIB-In.
 ///
 /// Handles both the legacy IPv4 NLRI fields and the MP_REACH/MP_UNREACH path