MINOR: server/event_hdl: add SERVER_INETADDR event

MINOR: server/event_hdl: add SERVER_INETADDR event

In this patch we add the support for a new SERVER event in the
event_hdl API.

SERVER_INETADDR is implemented as an advanced server event.
It is published each time the server's ip address or port is
about to change. (ie: from the cli, dns, lua...)

SERVER_INETADDR data is an event_hdl_cb_data_server_inetaddr struct
that provides additional info related to the server inet addr change,
but can be casted as a regular event_hdl_cb_data_server struct if
additional info is not needed.