MINOR: server/event_hdl: add server_inetaddr struct to facilitate event data usage

MINOR: server/event_hdl: add server_inetaddr struct to facilitate event data usage

event_hdl_cb_data_server_inetaddr struct had some anonymous structs
defined in it, making it impossible to pass as a function argument and
harder to maintain since changes must be performed at multiple places
at once. So instead we define a storage struct named server_inetaddr
that helps to save addr:port server information in INET context.

(cherry picked from commit 14893a6a00f24e14dcca5baa335a7f9d78dafc80)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>