tcp-passive: Clear connection on child closing

If this isn't done, then there may be invalid points left inside the
passive socket which could be used and cause a crash.

Fixes #33
1 job for <span class="ref-name">passive-close-child</span> in 51 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #47208
build-and-test

00:00:51