Fix critical unintentional variable name reuse

In `devp2p.discovery.recv_neighbours()` the variable `node` (ostensibly
containing the sender node) was reused as a temporary variable inside a 
for loop. 

Depending on the order of the `neighbours_lst` this lead in many cases
to neighbour information being attributed to the wrong sender node.

Thanks to @konradkonrad for the pair debugging :)

Refs: HydraChain/hydrachain#73

devp2p/discovery.py

@@ -489,24 +489,22 @@ def send_neighbours(self, node, neighbours):
  self.send(node, message)
 
  def recv_neighbours(self, nodeid, payload, mdc):
- node = self.get_node(nodeid)
+ remote = self.get_node(nodeid)
  assert len(payload) == 1
  neighbours_lst = payload[0]
  assert isinstance(neighbours_lst, list)
- log.debug('<<< neigbours', remoteid=node, count=len(neighbours_lst))
- neighbours = []
- neighbours_set = set(tuple(x) for x in neighbours_lst)
- if len(neighbours_set) < len(neighbours_lst):
- log.warn('received duplicates')
 
- for n in neighbours_set:
-  n = list(n)
+ neighbours = []
+ for n in neighbours_lst:
  nodeid = n.pop()
  address = Address.from_endpoint(*n)
  node = self.get_node(nodeid, address)
  assert node.address
  neighbours.append(node)
- self.kademlia.recv_neighbours(node, neighbours)
+
+ log.debug('<<< neighbours', remoteid=remote, local=self.this_node, neighbours=neighbours,
+ count=len(neighbours_lst))
+ self.kademlia.recv_neighbours(remote, neighbours)
 
 
 class NodeDiscovery(BaseService, DiscoveryProtocolTransport):