[addrman] Don't rebucket new table entries unnecessarily

Only rebucket if the asmap checksum has changed, not if the file format
has changed but no asmap is provided.

Also, don't try to add an entry to another bucket if it already appears
in ADDRMAN_NEW_BUCKETS_PER_ADDRESS buckets.

Author: jnewbery

src/addrman.h

@@ -517,6 +517,8 @@ friend class CAddrManTest;
             }
         }
 
+        // Attempt to restore the entry's new buckets if the bucket count and asmap
+        // checksum haven't changed
         uint256 supplied_asmap_checksum;
         if (m_asmap.size() != 0) {
             supplied_asmap_checksum = SerializeHash(m_asmap);
@@ -525,19 +527,26 @@ friend class CAddrManTest;
         if (format >= Format::V2_ASMAP) {
             s >> serialized_asmap_checksum;
         }
+        const bool restore_bucketing{nUBuckets == ADDRMAN_NEW_BUCKET_COUNT &&
+                                     serialized_asmap_checksum == supplied_asmap_checksum};
 
         for (auto bucket_entry : bucket_entries) {
             int bucket{bucket_entry.first};
             const int entry_index{bucket_entry.second};
             CAddrInfo& info = mapInfo[entry_index];
+
+            // The entry shouldn't appear in more than
+            // ADDRMAN_NEW_BUCKETS_PER_ADDRESS. If it has already, just skip
+            // this bucket_entry.
+            if (info.nRefCount >= ADDRMAN_NEW_BUCKETS_PER_ADDRESS) continue;
+
             int nUBucketPos = info.GetBucketPosition(nKey, true, bucket);
-            if (format >= Format::V2_ASMAP && nUBuckets == ADDRMAN_NEW_BUCKET_COUNT && vvNew[bucket][nUBucketPos] == -1 &&
-                info.nRefCount < ADDRMAN_NEW_BUCKETS_PER_ADDRESS && serialized_asmap_checksum == supplied_asmap_checksum) {
+            if (restore_bucketing && vvNew[bucket][nUBucketPos] == -1) {
                 // Bucketing has not changed, using existing bucket positions for the new table
                 vvNew[bucket][nUBucketPos] = entry_index;
                 info.nRefCount++;
             } else {
-                // In case the new table data cannot be used (format unknown, bucket count wrong or new asmap),
+                // In case the new table data cannot be used (bucket count wrong or new asmap),
                 // try to give them a reference based on their primary source address.
                 LogPrint(BCLog::ADDRMAN, "Bucketing method was updated, re-bucketing addrman entries from disk\n");
                 bucket = info.GetNewBucket(nKey, m_asmap);