[C10k] fix sender crash issue when test with 10K TCP connections
[C10k] fix sender crash issue when test with 10K TCP connections

The issue is, when test with 10K connections, such as -P 500 -n 20,
the sender side is not able to report test results in log;
instead, the sender side will exit with SIGPIPE (broken pipeline).

This issue has been fixed in this commit.

Microsoft/ntttcp-for-linux,Microsoft/ntttcp-for-linux