Merge bitcoin/bitcoin#29035: test: fix addnode functional test failure on OpenBSD

fd0bde2 test: fix `addnode` functional test failure on OpenBSD (Sebastian Falbesoner)

Pull request description:

  This is the functional test counterpart of PR #28891 / commit 007d6f0 (unfortunately, I missed it back then and only ran the unit tests -- sorry for the noise).

  master branch on OpenBSD 7.4:
  ```
  $ ./test/functional/rpc_net.py
  2023-12-08T17:29:05.057000Z TestFramework (INFO): PRNG seed is: 6024296850131317403
  2023-12-08T17:29:05.058000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_func_test_au3zchif
  2023-12-08T17:29:05.618000Z TestFramework (INFO): Test getconnectioncount
  2023-12-08T17:29:05.618000Z TestFramework (INFO): Test getpeerinfo
  2023-12-08T17:29:06.643000Z TestFramework (INFO): Check getpeerinfo output before a version message was sent
  2023-12-08T17:29:06.709000Z TestFramework (INFO): Test getnettotals
  2023-12-08T17:29:06.773000Z TestFramework (INFO): Test getnetworkinfo
  2023-12-08T17:29:06.978000Z TestFramework (INFO): Test addnode and getaddednodeinfo
  2023-12-08T17:29:06.980000Z TestFramework (ERROR): Assertion failed
  Traceback (most recent call last):
    File "/home/thestack/bitcoin/test/functional/test_framework/test_framework.py", line 131, in main
      self.run_test()
    File "/home/thestack/bitcoin/./test/functional/rpc_net.py", line 65, in run_test
      self.test_addnode_getaddednodeinfo()
    File "/home/thestack/bitcoin/./test/functional/rpc_net.py", line 224, in test_addnode_getaddednodeinfo
      assert_raises_rpc_error(-23, "Node already added", self.nodes[0].addnode, node=ip_port2, command='add')
    File "/home/thestack/bitcoin/test/functional/test_framework/util.py", line 131, in assert_raises_rpc_error
      assert try_rpc(code, message, fun, *args, **kwds), "No exception raised"
  AssertionError: No exception raised
  ```

  On the PR branch, the same call succeeds.

ACKs for top commit:
  kevkevinpal:
    ACK [fd0bde2](bitcoin/bitcoin@fd0bde2)

Tree-SHA512: ae20816fa4025c212e115ebd267b5e5784bfcdf0051219eb686faaade47ec4f91a3947af6d24258b159290000d2dcc3f6e65e788b83b8a9297282945dbdafbfb

Author: fanquake

test/functional/rpc_net.py

@@ -9,6 +9,7 @@
 
 from decimal import Decimal
 from itertools import product
+import platform
 import time
 
 import test_framework.messages
@@ -220,8 +221,10 @@ def test_addnode_getaddednodeinfo(self):
         ip_port = "127.0.0.1:{}".format(p2p_port(2))
         self.nodes[0].addnode(node=ip_port, command='add')
         # try to add an equivalent ip
-        ip_port2 = "127.1:{}".format(p2p_port(2))
-        assert_raises_rpc_error(-23, "Node already added", self.nodes[0].addnode, node=ip_port2, command='add')
+        # (note that OpenBSD doesn't support the IPv4 shorthand notation with omitted zero-bytes)
+        if platform.system() != "OpenBSD":
+            ip_port2 = "127.1:{}".format(p2p_port(2))
+            assert_raises_rpc_error(-23, "Node already added", self.nodes[0].addnode, node=ip_port2, command='add')
         # check that the node has indeed been added
         added_nodes = self.nodes[0].getaddednodeinfo()
         assert_equal(len(added_nodes), 1)