Merge bitcoin/bitcoin#26265: POLICY: Relax MIN_STANDARD_TX_NONWITNESS_SIZE to 65 non-witness bytes

b2aa9e8528 Add release note for MIN_STANDARD_TX_NONWITNESS_SIZE relaxation (Greg Sanders)
8c5b3646b5 Relax MIN_STANDARD_TX_NONWITNESS_SIZE to 65 non-witness bytes (Greg Sanders)

Pull request description:

  Since the original fix was set to be a "reasonable" transaction to reduce allocations and the true motivation later revealed, it makes sense to relax this check to something more principled.

  There are more exotic transaction patterns that could take advantage of a relaxed requirement, such as 1 input, 1 output OP_RETURN to burn a utxo to fees for CPFP purposes when change isn't practical.

  Two changes could be accomplished:

  1) Anything not 64 bytes could be allowed

  2) Anything above 64 bytes could be allowed

  In the Great Consensus Cleanup, suggestion (2)
  was proposed as a consensus change, and is the simpler of the two suggestions. It would not allow an "empty" OP_RETURN but would reduce the required padding from 22 bytes to 5.

  The functional test is also modified to test the actual case
  we care about: 64 bytes

  Related mailing list discussions here:
  https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-October/020995.html
  And a couple years earlier:
  https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-May/017883.html

ACKs for top commit:
  achow101:
    reACK b2aa9e8528
  glozow:
    reACK b2aa9e8528
  pablomartin4btc:
    re-ACK b2aa9e8528
  jonatack:
    ACK b2aa9e8528 with some suggestions

Tree-SHA512: c1ec1af9ddcf31b2272209a4f1ee0c5607399f8172e5a1dfd4604cf98bfb933810dd9369a5917ad122add003327c9fcf6ee26995de3aca41d5c42dba527991ad

doc/release-notes-26265.md

@@ -0,0 +1,6 @@
+P2P and network changes
+---------
+
+- Transactions of non-witness size 65 and above are now allowed by mempool
+  and relay policy. This is to better reflect the actual afforded protections
+  against CVE-2017-12842 and open up additional use-cases of smaller transaction sizes. (#26265)