blocksonly nodes don't benefit from compact blocks, since they don't
have a mempool to aid in reconstruction, so they should not process
CMPCTBLOCK messages.
This is not just belt-and-suspenders, as a blocksonly node will
trivially reveal exactly which transactions in a block are its own in
the GETBLOCKTXN response to a CMPCTBLOCK. Since it will be missing every
transaction in the block, except for its own.
See discussion: https://github.com/bitcoin/bitcoin/issues/28272
Note that we unfortunately can't use a scripted diff here, as the
`sha256` symbol is also used for other instances (e.g. as function
in hashlib, or in the `UTXO` class in p2p_segwit.py).
Since the previous commit, CBlockHeader/CBlock object calls to the
methods `.rehash()` and `.calc_sha256()` are effectively no-ops
if the returned value is not used, so we can just remove them.
send_message only drops the bytes in a buffer and a sync is needed to
avoid intermittent test issues. Change the name of the method to make
this more apparent during review.
-BEGIN VERIFY SCRIPT-
sed -i 's/send_message(/send_without_ping(/g' $( git grep -l 'send_message(' )
-END VERIFY SCRIPT-
