pytest: make test_gossip_throttle more reliable.

By having gossipwith filter out messages we don't want, we can get the counts of
expected messages correct, and not hit errors like this:

```
    def test_gossip_throttle(node_factory, bitcoind, chainparams):
        """Make some gossip, test it gets throttled"""
        l1, l2, l3, l4 = node_factory.line_graph(4, wait_for_announce=True,
                                                 opts=[{}, {}, {}, {'dev-throttle-gossip': None}])
    
        # We expect: self-advertizement (3 messages for l1 and l4) plus
        # 4 node announcements, 3 channel announcements and 6 channel updates.
        # We also expect it to send a timestamp filter message.
        # (We won't take long enough to get a ping!)
        expected = 4 + 4 + 3 + 6 + 1
    
        # l1 is unlimited
        start_fast = time.time()
        out1 = subprocess.run(['devtools/gossipwith',
                               '--all-gossip',
                               '--hex',
                               '--network={}'.format(TEST_NETWORK),
                               '--max-messages={}'.format(expected),
                               '{}@localhost:{}'.format(l1.info['id'], l1.port)],
                              check=True,
                              timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
        time_fast = time.time() - start_fast
        assert time_fast < 2
        # Remove timestamp filter, since timestamp will change!
        out1 = [m for m in out1 if not m.startswith(b'0109')]
    
        # l4 is throttled
        start_slow = time.time()
        out2 = subprocess.run(['devtools/gossipwith',
                               '--all-gossip',
                               '--hex',
                               '--network={}'.format(TEST_NETWORK),
                               '--max-messages={}'.format(expected),
                               '{}@localhost:{}'.format(l4.info['id'], l4.port)],
                              check=True,
                              timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
        time_slow = time.time() - start_slow
        assert time_slow > 3
    
        # Remove timestamp filter, since timestamp will change!
        out2 = [m for m in out2 if not m.startswith(b'0109')]
    
        # Contents should be identical (once uniquified, since each
        # doubles-up on its own gossip)
>       assert set(out1) == set(out2)
E       AssertionError: assert {b'010054b1907bdf639c9060e0fa4bca02419c46f75a99f0908b87a2e09711d5d031ba76b8fd07acc8be1b2fac9e31efb808e5d362c32ef4665...
E         Extra items in the left set:
E         b'01010ad5be8b9ba029245c2ae2d667af7ead7c0129c479c7fd7145a9b65931e90222082e6e4ab37ef60ebd10f1493d73e8bf7a40c4ae5f7d87cc...8488830b60f7e744ed9235eb0b1ba93283b315c035180266e44a554e494f524245414d2d333930353033622d6d6f64646564000000000000000000'
E         Extra items in the right set:
E         b'01079f87eb580b9e5f11dc211e9fb66abb3699999044f8fe146801162393364286c6000000010000006c010101'
```

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

tests/test_gossip.py

@@ -2058,41 +2058,36 @@ def test_gossip_throttle(node_factory, bitcoind, chainparams):
 
     # We expect: self-advertizement (3 messages for l1 and l4) plus
     # 4 node announcements, 3 channel announcements and 6 channel updates.
-    # We also expect it to send a timestamp filter message.
-    # (We won't take long enough to get a ping!)
-    expected = 4 + 4 + 3 + 6 + 1
+    expected = 4 + 4 + 3 + 6
 
     # l1 is unlimited
     start_fast = time.time()
     out1 = subprocess.run(['devtools/gossipwith',
                            '--all-gossip',
                            '--hex',
                            '--network={}'.format(TEST_NETWORK),
+                           '--filter=256,257,258',
                            '--max-messages={}'.format(expected),
                            '{}@localhost:{}'.format(l1.info['id'], l1.port)],
                           check=True,
                           timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
     time_fast = time.time() - start_fast
     assert time_fast < 2
-    # Remove timestamp filter, since timestamp will change!
-    out1 = [m for m in out1 if not m.startswith(b'0109')]
 
     # l4 is throttled
     start_slow = time.time()
     out2 = subprocess.run(['devtools/gossipwith',
                            '--all-gossip',
                            '--hex',
                            '--network={}'.format(TEST_NETWORK),
+                           '--filter=256,257,258',
                            '--max-messages={}'.format(expected),
                            '{}@localhost:{}'.format(l4.info['id'], l4.port)],
                           check=True,
                           timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
     time_slow = time.time() - start_slow
     assert time_slow > 3
 
-    # Remove timestamp filter, since timestamp will change!
-    out2 = [m for m in out2 if not m.startswith(b'0109')]
-
     # Contents should be identical (once uniquified, since each
     # doubles-up on its own gossip)
     assert set(out1) == set(out2)
@@ -2121,30 +2116,29 @@ def test_gossip_throttle(node_factory, bitcoind, chainparams):
                            '--no-gossip',
                            '--hex',
                            '--network={}'.format(TEST_NETWORK),
-                           '--max-messages={}'.format(expected + 1),
+                           '--filter=256,257,258',
+                           '--max-messages={}'.format(expected),
                            '{}@localhost:{}'.format(l1.info['id'], l1.port),
                            query],
                           check=True,
                           timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
     time_fast = time.time() - start_fast
     assert time_fast < 2
-    # Ignore gossip_timestamp_filter and reply_short_channel_ids_end
-    out3 = [m for m in out3 if not m.startswith(b'0109') and not m.startswith(b'0106')]
     assert set(out1) == set(out3)
 
     start_slow = time.time()
     out4 = subprocess.run(['devtools/gossipwith',
                            '--no-gossip',
                            '--hex',
                            '--network={}'.format(TEST_NETWORK),
+                           '--filter=256,257,258',
                            '--max-messages={}'.format(expected),
                            '{}@localhost:{}'.format(l4.info['id'], l4.port),
                            query],
                           check=True,
                           timeout=TIMEOUT, stdout=subprocess.PIPE).stdout.split()
     time_slow = time.time() - start_slow
     assert time_slow > 3
-    out4 = [m for m in out4 if not m.startswith(b'0109')]
     assert set(out2) == set(out4)