Merge bitcoin/bitcoin#30705: test: Avoid intermittent block download timeout in p2p_ibd_stalling

fa5b58e test: Avoid intermittent block download timeout in p2p_ibd_stalling (MarcoFalke)

Pull request description:

  Fixes #30704

  The goal of the test is to check the stalling timeout, not the block download timeout.

  On extremely slow hardware (for example qemu virtual hardware), downloading the 1023 blocks may take longer than the block download timeout.

  Fix it by pinning the time using mocktime, and only advance it when testing the stalling timeout.

ACKs for top commit:
  tdb3:
    CR ACK fa5b58e
  brunoerg:
    utACK fa5b58e

Tree-SHA512: 9a9221f264bea52be5e9fe81fd319f5a6970cd315cc5e9f5e2e049c5d84619b19b9f6f075cda8d34565c2d6c17a88fb57e195c66c271e40f73119a77caecb6d7

Author: fanquake

test/functional/p2p_ibd_stalling.py

@@ -73,6 +73,7 @@ def run_test(self):
         peers = []
 
         self.log.info("Check that a staller does not get disconnected if the 1024 block lookahead buffer is filled")
+        self.mocktime = int(time.time()) + 1
         for id in range(NUM_PEERS):
             peers.append(node.add_outbound_p2p_connection(P2PStaller(stall_block), p2p_idx=id, connection_type="outbound-full-relay"))
             peers[-1].block_store = block_dict
@@ -85,7 +86,7 @@ def run_test(self):
 
         self.all_sync_send_with_ping(peers)
         # If there was a peer marked for stalling, it would get disconnected
-        self.mocktime = int(time.time()) + 3
+        self.mocktime += 3
         node.setmocktime(self.mocktime)
         self.all_sync_send_with_ping(peers)
         assert_equal(node.num_test_p2p_connections(), NUM_PEERS)