Disable bloom filtering by default.

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.

test/functional/test_framework/messages.py

@@ -44,7 +44,7 @@ BIP125_SEQUENCE_NUMBER = 0xfffffffd  # Sequence number that is BIP 125 opt-in an
 
 NODE_NETWORK = (1 << 0)
 # NODE_GETUTXO = (1 << 1)
-NODE_BLOOM = (1 << 2)
+# NODE_BLOOM = (1 << 2)
 NODE_WITNESS = (1 << 3)
 NODE_NETWORK_LIMITED = (1 << 10)