protocol: detect and drop asshole peers

defined as those who don't relay blocks for now.

Using transactions would be much faster, but more error prone,
as well as exploit prone.

The score can be reused later to store in the peer list to
affect selection probability.

+    {
+      MINFO(context << "Peer " << context.m_connection_id << " relayed the block we were waiting on");
+      context.m_score += 1;
+      if (context.m_score > 10) // prevent a node from being all nice for a while then switching to asshole

+    {
+      if (!m_p2p->for_connection(uuid, [&](cryptonote_connection_context& ctx, nodetool::peerid_type peer_id, uint32_t f)->bool{
+        MINFO(ctx << "dropping bad peer (score " << ctx.m_score << ")");
+        drop_connection(ctx, 10, false);