Since Linux 4.5, sendmsg(2) fails with ETOOMANYREFS if the number of
"in-flight" IOs, which has been sent by sendmsg(2) but has not yet
accepted by recvmsg(2), exceeds the RLIMIT_NOFILE resource limit.

https://rubyci.s3.amazonaws.com/arm64-neoverse-n1/ruby-master/log/20231025T090004Z.fail.html.gz
```
  1) Error:
TestSocket_UNIXSocket#test_fd_passing_race_condition:
Errno::ETOOMANYREFS: Too many references: cannot splice - sendmsg(2)
```

This change reduces the number of times of IO passing under 1024,
which is a default limit in many environments.