The discouragement threshold is modified to account for the change in
D6036, which caused a peer to be banned after only 10 out-of-order messages
instead of 100.
Using the wrong value in this test could potentially cause the node to
be banned before all messages are sent, and cause the next
`self.send_message(msg_verack())` because this method fails when trying
to send a message if the connection is closed.
I observed this failure while trying core#19657 (D10063), in which the
message is sent a bit later in the test and the node bans the p2p
connection faster.