[mac] Modify Mac default timeout for TIME_WAIT

macOS has only 16K ports available that won't be released until socket

TIME_WAIT is passed. The default timeout for TIME_WAIT is 15 seconds.

Consider reducing in case of available port bottleneck.

You can check whether this is a problem with netstat:

    # sysctl net.inet.tcp.msl

    net.inet.tcp.msl: 15000

    # sudo sysctl -w net.inet.tcp.msl=1000

    net.inet.tcp.msl: 15000 -> 1000

Run siege.config to create the ~/.siegerc config file.