Merge #16152: Disable bloom filtering by default.

bead32e31e Add release notes for DEFAULT_BLOOM change (Matt Corallo)
f27309f55c Move DEFAULT_PEERBLOOMFILTERS from validation.h to net_processing.h (Matt Corallo)
5efcb77283 Disable bloom filtering by default. (Matt Corallo)

Pull request description:

  BIP 37 bloom filters have been well-known to be a significant DoS
  target for some time. However, in order to provide continuity for
  SPV clients relying on it, the NODE_BLOOM service flag was added,
  and left as a default, to ensure sufficient nodes exist with such a
  flag.

  NODE_BLOOM is, at this point, well-established and, as long as
  there exist 0.18 nodes with default config (which I'd anticipate
  will be true for many years), will be available from some peers. By
  that time, the continued slowdown of BIP 37-based filtering will
  likely have rendered it useless (though this is already largely the
  case). Further, BIP 37 was deliberately never updated to support
  witness-based filtering as newer wallets are expected to migrate to
  some yet-to-be-network-exposed filters.

ACKs for top commit:
  jnewbery:
    ACK bead32e31e
  kallewoof:
    ACK bead32e31e

Tree-SHA512: ecd901898e8efe1a7c82b471af0acc2373c2282ac633eb58d9aae7c35deda1999d0f79fb0485e6cecbda7246aeda00206cd82c7fa36866e2ac64705ba93f9390

doc/release-notes/release-notes-16152.md

@@ -0,0 +1,7 @@
+P2P Changes
+-----------
+- The default value for the -peerbloomfilters configuration option (and, thus, NODE_BLOOM support) has been changed to false.
+  This resolves well-known DoS vectors in Bitcoin Core, especially for nodes with spinning disks. It is not anticipated that
+  this will result in a significant lack of availability of NODE_BLOOM-enabled nodes in the coming years, however, clients
+  which rely on the availability of NODE_BLOOM-supporting nodes on the P2P network should consider the process of migrating
+  to a more modern (and less trustful and privacy-violating) alternative over the coming years.