test: Fix intermittent failure in p2p_v2_misbehaving.py

The ellswift bytes are computed in the NetworkThread and sent in
the MainThread. Add a `wait_until()` to make sure that ellswift
computation is completed in NetworkThread before sending it in
the MainThread.

Author: stratospher

test/functional/p2p_v2_misbehaving.py

@@ -143,6 +143,7 @@ def test_earlykeyresponse(self):
         self.log.info('Sending remaining ellswift and garbage which are different from V1_PREFIX. Since a response is')
         self.log.info('expected now, our custom data_received() function wouldn\'t result in assertion failure')
         peer1.v2_state.can_data_be_received = True
+        self.wait_until(lambda: peer1.v2_state.ellswift_ours)
         peer1.send_raw_message(peer1.v2_state.ellswift_ours[4:] + peer1.v2_state.sent_garbage)
         with node0.assert_debug_log(['V2 handshake timeout peer=0']):
             peer1.wait_for_disconnect(timeout=5)