170004 is the protocol version for the NODE_BLOOM change, which is being
"released" in this RC. The activation height is being set in the final release,
which means that we may end up with both RC and final release versions online
when Overwinter activates. Bumping the protocol version for Overwinter enables
RC nodes to be correctly disconnected.
An example of where this might be useful is allowing a node to connect blocksonly during IBD but then becoming a full-node once caught up with the latest block. This might also even want to be the default behaviour since during IBD most TXs appear to be orphans, and are routinely dropped (for example when a node disconnects). Therefore, this can waste a lot of bandwidth.
Additionally, another pull could be written to stop relaying of TXs to nodes that are clearly far behind the latest block and are running a node that doesn't store many orphan TXs, such as recent versions of Bitcoin Core.
Previously peers which implement a protocol version less than NO_BLOOM_VERSION
would not be disconnected for sending a filter command, regardless of the
peerbloomfilter option.
Many node operators do not wish to provide expensive bloom filtering for SPV
clients, previously they had to cherry pick the commit which enabled the
disconnect logic.
The default should remain false until a sufficient percent of SPV clients
have updated.
