test: Fix intermittent issue in p2p_addr_relay.py

by increasing the mocktime bump for m_next_addr_send, which is on a
Poisson timer, and explain why. Closes #22449

Author: mzumsande

test/functional/p2p_addr_relay.py

@@ -121,7 +121,10 @@ def setup_rand_addr_msg(self, num):
 
     def send_addr_msg(self, source, msg, receivers):
         source.send_and_ping(msg)
-        # pop m_next_addr_send timer
+        # invoke m_next_addr_send timer:
+        # `addr` messages are sent on an exponential distribution with mean interval of 30s.
+        # Setting the mocktime 600s forward gives a probability of (1 - e^-(600/30)) that
+        # the event will occur (i.e. this fails once in ~500 million repeats).
         self.mocktime += 10 * 60
         self.nodes[0].setmocktime(self.mocktime)
         for peer in receivers:
@@ -282,7 +285,8 @@ def getaddr_tests(self):
         block_relay_peer.send_and_ping(msg_getaddr())
         inbound_peer.send_and_ping(msg_getaddr())
 
-        self.mocktime += 5 * 60
+        # invoke m_next_addr_send timer, see under send_addr_msg() function for rationale
+        self.mocktime += 10 * 60
         self.nodes[0].setmocktime(self.mocktime)
         inbound_peer.wait_until(lambda: inbound_peer.addr_received() is True)