make sure the TCP listeners are dropped after sening them via SCM_RIGHTS
make sure the TCP listeners are dropped after sening them via SCM_RIGHTS

sending a socket with SCM_RIGHTS is equivalent to calling dup(), so if
the listener is not closed after sending, it will still be valid until
the worker process is closed, which could take a while. So we use
as_raw_fd() to send the file desriptor with SCM_RIGHTS, then let the
listener be dropped afterwards

sozu-proxy/sozu,sozu-proxy/sozu,sozu-proxy/sozu