To restart ssh/sshd service in Mac OS X, you can simply run the following two commands together:
sudo launchctl stop com.openssh.sshd sudo launchctl start com.openssh.sshd
Your sshd will get restarted and your new ssh config file can be loaded as well.
p.s. Friendly reminding: DO NOT try to execute
sudo launchctl reboot com.openssh.sshd
instead since your computer will immediately get rebooted 🙂