Rather than only setting the services field for inbound peers, set it for
all peers. This field referes to the remote peer's services regardless of
inbound or outbound.
This commit significantly reworks the fetching code to interop better with
bitcoind. In particular, when an inventory message is sent, and the
remote peer requests the final block, the remote peer sends the current
end of the main chain to signal that there are more blocks to get.
Previously this code was automatically requesting more blocks when the
number of in-flight blocks was under a certain threshold. The original
approach does help alleviate delays in the "request final, wait for
orphan, request more" round trip, but due to the aforementioned mechanism,
it leads to double requests and other subtle issues.
This commit modifies the input message handler so that when a remote peer
sends a block, no further messages from that peer are accepted until the
block has been fully processed and therefore known good or bad. This
helps prevent a malicious peer from queueing up a bunch of bad blocks
before disconnecting (or being disconnected) and wasting memory.
Additionally, this behavior is depended on by at least the block
acceptance test tool as the reference implementation processes blocks in
the same thread and therefore blocks further messages until the block has
been fully processed as well.
