fix EADDRINUSE when reloading with tcp socket enabled

[sni]

without the SO_REUSEADDR / SO_REUSEPORT option lingering TIME_WAIT connections will prevent naemon from loading the module after a reload.

for details see:

• https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ
• https://developer.ibm.com/tutorials/l-sockpit/#pitfall-3-address-in-use-error-eaddrinuse-

to reproduce, start naemon and send a keepalive query to livestatus. Naemon will then stop when trying to reload with 'Unable to bind to...' error.

[sni]

i added the ifdef since i need it for rhel6 anyway :-)