Remove address book peers that have changed to clients

If an address book peer stops advertising the NODE_SERVICES bit, remove
it from the address book.

zebra-network/src/address_book.rs

@@ -139,7 +139,15 @@ impl AddressBook {
             recent_peers = self.recently_live_peers().count(),
         );
 
-        // Drop any unspecified or client addresses.
+        // If a node that we are directly connected to has changed to a client,
+        // remove it from the address book.
+        if new.is_direct_client() && self.contains_addr(&new.addr) {
+            std::mem::drop(_guard);
+            self.take(new.addr);
+            return;
+        }
+
+        // Never add unspecified addresses or client services.
         //
         // Communication with these addresses can be monitored via Zebra's
         // metrics. (The address book is for valid peer addresses.)

zebra-network/src/meta_addr.rs

@@ -156,7 +156,9 @@ impl MetaAddr {
     ///
     /// # Security
     ///
-    /// This address must be the remote address from an outbound connection.
+    /// This address must be the remote address from an outbound connection,
+    /// and the services must be the services from that peer's handshake.
+    ///
     /// Otherwise:
     /// - malicious peers could interfere with other peers' `AddressBook` state,
     ///   or
@@ -226,6 +228,14 @@ impl MetaAddr {
         self.last_seen
     }
 
+    /// Is this address a directly connected client?
+    pub fn is_direct_client(&self) -> bool {
+        match self.last_connection_state {
+            Responded => !self.services.contains(PeerServices::NODE_NETWORK),
+            NeverAttemptedGossiped | NeverAttemptedAlternate | Failed | AttemptPending => false,
+        }
+    }
+
     /// Is this address valid for outbound connections?
     pub fn is_valid_for_outbound(&self) -> bool {
         self.services.contains(PeerServices::NODE_NETWORK)