Merge bitcoin#29704: test: make p2p_handshake robust against timeoffset warnings

032a597 test: make p2p_handshake robust against timeoffset warnings (stickies-v)

Pull request description:

  The new `p2p_handshake` test requires that limited nodes are not peered with when the node's system time exceeds ~ 24h of the node's chaintip timestamp, as per [`PeerManagerImpl::GetDesirableServiceFlags`](https://github.com/bitcoin/bitcoin/blob/2ffaa927023f5dc2a7b8d6cfeb4f4810e573b18c/src/net_processing.cpp#L1717).

  By patching this test to modify the timestamp of the chaintip as opposed to mocking the node's system time, we make it resilient to future commits where the node raises a warning if it detects its system time is too much out of sync with its outbound peers.

  Resolves a silent merge conflict in bitcoin#29623, that is changing the warning behaviour when significant time differences with outbound peers are detected, [failing the test as it's currently in master](https://cirrus-ci.com/task/6553996884705280?logs=ci#L4666).

  Considerations/alternatives I've thought of:
  - could add `self.setup_clean_chain = True` to `self.set_test_params()`, to avoid creating a new tip with a (much) older date, but it doesn't seem to matter?
  - could avoid using `setmocktime` altogether and instead use [`create_block`](https://github.com/bitcoin/bitcoin/blob/2ffaa927023f5dc2a7b8d6cfeb4f4810e573b18c/test/functional/test_framework/blocktools.py#L68) instead, but that seems like it'll be a lot more verbose and I don't think it's worth it?

  Big thanks to theStack for his time in discussing this with me offline.

ACKs for top commit:
  maflcko:
    lgtm ACK 032a597
  theStack:
    ACK 032a597
  brunoerg:
    crACK 032a597
  BrandonOdiwuor:
    Code Review ACK 032a597

Tree-SHA512: 407564754a100bc9252f5737182de2e111993944ec9a0463a4a43195ce98cd1119de982c8fe5f7531ddb56603043812bf7bf2163a780d30b6df03a072c3308c3

Author: fanquake

test/functional/p2p_handshake.py

@@ -62,6 +62,11 @@ def test_desirable_service_flags(self, node, service_flag_tests, desirable_servi
                 assert (services & desirable_service_flags) == desirable_service_flags
                 self.add_outbound_connection(node, conn_type, services, wait_for_disconnect=False)
 
+    def generate_at_mocktime(self, time):
+        self.nodes[0].setmocktime(time)
+        self.generate(self.nodes[0], 1)
+        self.nodes[0].setmocktime(0)
+
     def run_test(self):
         node = self.nodes[0]
         self.log.info("Check that lacking desired service flags leads to disconnect (non-pruned peers)")
@@ -71,10 +76,10 @@ def run_test(self):
                                           DESIRABLE_SERVICE_FLAGS_FULL, expect_disconnect=False)
 
         self.log.info("Check that limited peers are only desired if the local chain is close to the tip (<24h)")
-        node.setmocktime(int(time.time()) + 25 * 3600)  # tip outside the 24h window, should fail
+        self.generate_at_mocktime(int(time.time()) - 25 * 3600)  # tip outside the 24h window, should fail
         self.test_desirable_service_flags(node, [NODE_NETWORK_LIMITED | NODE_WITNESS],
                                           DESIRABLE_SERVICE_FLAGS_FULL, expect_disconnect=True)
-        node.setmocktime(int(time.time()) + 23 * 3600)  # tip inside the 24h window, should succeed
+        self.generate_at_mocktime(int(time.time()) - 23 * 3600)  # tip inside the 24h window, should succeed
         self.test_desirable_service_flags(node, [NODE_NETWORK_LIMITED | NODE_WITNESS],
                                           DESIRABLE_SERVICE_FLAGS_PRUNED, expect_disconnect=False)