MINOR: Add TLS ticket keys reference and use it in the listener struct

MINOR: Add TLS ticket keys reference and use it in the listener struct

Within the listener struct we need to use a reference to the TLS
ticket keys which binds the actual keys with the filename. This will
make it possible to update the keys through the socket

Signed-off-by: Nenad Merdanovic <nmerdan@anine.io>