TEST: Enable TCP blackhole on Cirrus CI to test this PR

This commit must be removed from the final fix.

Author: vstinner

.cirrus.yml

@@ -7,9 +7,9 @@ freebsd_task:
   # local local connections to fail with ETIMEDOUT instead of ECONNREFUSED.
   # For more information see https://reviews.freebsd.org/D41751 and
   # https://github.com/cirruslabs/cirrus-ci-docs/issues/483.
-  sysctl_script:
-    - sysctl net.inet.tcp.blackhole=0
-    - sysctl net.inet.udp.blackhole=0
+#  sysctl_script:
+#    - sysctl net.inet.tcp.blackhole=0
+#    - sysctl net.inet.udp.blackhole=0
   build_script:
     - mkdir build
     - cd build