traffic_manager can't bind to port 80 sometimes.

During new install/updates sometimes, when ATS is restarted too quickly multiple times, we occasionally end up with the below error, causing ATS not to come up:

[Jun 11 14:46:24.852] Manager {0x7fa0e2b217e0} NOTE: [LocalManager::listenForProxy] Listening on port: 80
[Jun 11 14:46:24.852] Manager {0x7fa0e2b217e0} NOTE: [LocalManager::listenForProxy] Listening on port: 443
[Jun 11 14:46:24.852] Manager {0x7fa0e2b217e0} ERROR: [bindProxyPort] Unable to bind socket: 80 : Address already in use

This is quite annoying and inconvenient since it blocks ATS from coming up (sometimes for very long) until a reboot or some other deep clean up is performed.

Would like to add the socket option SO_REUSEPORT to the socket doing the proxy port binding.