Merge #11025: qa: Fix inv race in example_test

faa76d1b7 qa: Fix inv race in example_test (MarcoFalke)

Pull request description:

  There have been intermittent test failures on this script.

  ```py
    File "./test/functional/example_test.py", line 216, in run_test
      assert_equal(block, 1)
  AssertionError: not(2 == 1)
  ```

  Probably the simplest way to fix them is overriding the `on_inv` method, so that no "colliding" getdata for the blocks are sent out.

  Additionally, all getdata are now sent in a single message.

Tree-SHA512: 809c2bbfa90a67fc97905769fcbe90ba9abe1aac1f145530934f56a364835973b94d3302b6be68f4f2987acf333bce146bcc4c878c283301871ba5bb1a9bedb6

test/functional/example_test.py

@@ -58,6 +58,10 @@ class BaseNode(NodeConnCB):
         message.block.calc_sha256()
         self.block_receive_map[message.block.sha256] += 1
 
+    def on_inv(self, conn, message):
+        """Override the standard on_inv callback"""
+        pass
+
 def custom_function():
     """Do some custom behaviour
 
@@ -198,10 +202,10 @@ class ExampleTest(BitcoinTestFramework):
 
         self.log.info("Wait for node2 reach current tip. Test that it has propogated all the blocks to us")
 
+        getdata_request = msg_getdata()
         for block in blocks:
-            getdata_request = msg_getdata()
             getdata_request.inv.append(CInv(2, block))
-            node2.send_message(getdata_request)
+        node2.send_message(getdata_request)
 
         # wait_until() will loop until a predicate condition is met. Use it to test properties of the
         # NodeConnCB objects.