test: Add imports for util bpf_cflags

This is required for the next commit.

test/functional/interface_usdt_net.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright (c) 2022 The Bitcoin Core developers
+# Copyright (c) 2022-present The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -17,7 +17,11 @@ except ImportError:
 from test_framework.messages import CBlockHeader, MAX_HEADERS_RESULTS, msg_headers, msg_version
 from test_framework.p2p import P2PInterface
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal, assert_greater_than
+from test_framework.util import (
+    assert_equal,
+    assert_greater_than,
+    bpf_cflags,
+)
 
 # Tor v3 addresses are 62 chars + 6 chars for the port (':12345').
 MAX_PEER_ADDR_LENGTH = 68