Don't trust reported peer `last_seen` times

Due to clock skew, the peers could end up at the front of the
reconnection queue or far at the back. The solution to this is to offset
the reported times by the difference between the most recent reported
sight (in the remote clock) and the current time (in the local clock).

zebra-network/src/peer_set/candidate_set.rs

@@ -330,9 +330,10 @@ where
 /// If the data in an address is invalid, this function can:
 /// - modify the address data, or
 /// - delete the address.
-//
-// TODO: re-enable this lint when last_seen_limit is used
-#[allow(unused_variables)]
+///
+/// Currently, this method will offset the reported `last_seen` time to prevent clock skews
+/// from causing the peers to be placed too far back or in the front of the reconnection queue
+/// incorrectly.
 fn validate_addrs(
     addrs: impl IntoIterator<Item = MetaAddr>,
     last_seen_limit: DateTime32,
@@ -342,12 +343,35 @@ fn validate_addrs(
 
     // TODO:
     // We should eventually implement these checks in this function:
-    // - Zebra should stop believing far-future last_seen times from peers (#1871)
     // - Zebra should ignore peers that are older than 3 weeks (part of #1865)
     //   - Zebra should count back 3 weeks from the newest peer timestamp sent
     //     by the other peer, to compensate for clock skew
     // - Zebra should limit the number of addresses it uses from a single Addrs
     //   response (#1869)
 
+    let mut addrs: Vec<_> = addrs.into_iter().collect();
+
+    if !addrs.is_empty() {
+        limit_last_seen_times(&mut addrs, last_seen_limit);
+    }
+
     addrs.into_iter()
 }
+
+/// Ensure all reported `last_seen` times are less than or equal to `last_seen_limit`.
+///
+/// This function assumes there is at least one address in the `addrs` list.
+fn limit_last_seen_times(addrs: &mut Vec<MetaAddr>, last_seen_limit: DateTime32) {
+    let most_recent_reported_seen_time = addrs
+        .iter()
+        .map(|addr| addr.get_last_seen())
+        .max()
+        .expect("unexpected empty address list");
+
+    let offset = most_recent_reported_seen_time.timestamp() - last_seen_limit.timestamp();
+
+    for addr in addrs {
+        let last_seen = addr.get_last_seen().timestamp() - offset;
+        addr.set_last_seen(last_seen.into());
+    }
+}