message: [addrman] Rename asmap version to asmap checksum
  Version implies that higher numbers take precendence. This is really a
  checksum, to check whether the provided asmap is the same as the one
  used when the peers.dat file was serialized.
  Also update the comments to explain where/why this is used.
diff: @@ -340,6 +340,7 @@ public:
  * * for each bucket:
  * * number of elements
  * * for each element: index
  + * * asmap checksum
  *
  * 2**30 is xorred with the number of buckets to make addrman deserializer v0 detect it
  * as incompatible. This is necessary because it did not check the version number on
  @@ -348,8 +349,8 @@ public:
  * Notice that vvTried, mapAddr and vVector are never encoded explicitly;
  * they are instead reconstructed from the other information.
  *
  - * vvNew is serialized, but only used if ADDRMAN_UNKNOWN_BUCKET_COUNT didn't change,
  - * otherwise it is reconstructed as well.
  + * vvNew is serialized, but only used if ADDRMAN_NEW_BUCKET_COUNT and the asmap checksum
  + * didn't change, otherwise it is reconstructed as well.
  *
  * This format is more complex, but significantly smaller (at most 1.5 MiB), and supports
  * changes to the ADDRMAN_ parameters without breaking the on-disk structure.
  @@ -413,13 +414,13 @@ public:
  }
  }
  }
  - // Store asmap version after bucket entries so that it
  + // Store asmap checksum after bucket entries so that it
  // can be ignored by older clients for backward compatibility.
  - uint256 asmap_version;
  + uint256 asmap_checksum;
  if (m_asmap.size() != 0) {
  - asmap_version = SerializeHash(m_asmap);
  + asmap_checksum = SerializeHash(m_asmap);
  }
  - s << asmap_version;
  + s << asmap_checksum;
  }
  template <typename Stream>
  @@ -516,13 +517,13 @@ public:
  }
  }
  - uint256 supplied_asmap_version;
  + uint256 supplied_asmap_checksum;
  if (m_asmap.size() != 0) {
  - supplied_asmap_version = SerializeHash(m_asmap);
  + supplied_asmap_checksum = SerializeHash(m_asmap);
  }
  - uint256 serialized_asmap_version;
  + uint256 serialized_asmap_checksum;
  if (format >= Format::V2_ASMAP) {
  - s >> serialized_asmap_version;
  + s >> serialized_asmap_checksum;
  }
  for (auto bucket_entry : bucket_entries) {
  @@ -531,7 +532,7 @@ public:
  CAddrInfo& info = mapInfo[entry_index];
  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_version == supplied_asmap_version) {
  + info.nRefCount < ADDRMAN_NEW_BUCKETS_PER_ADDRESS && serialized_asmap_checksum == supplied_asmap_checksum) {
  // Bucketing has not changed, using existing bucket positions for the new table
  vvNew[bucket][nUBucketPos] = entry_index;
  info.nRefCount++;
  