network: add timeout for client connections

Somtimes client connetions will not close therfore add a timeout. Add a
new timer that checks every 5s if we did not receive anything from a
client for (default) 60s. Can be configured via client_timeout.

Code is based on the work of ptpt52.

Signed-off-by: Nick Hainke <vincent@systemli.org>

src/include/datastorage.h

@@ -109,6 +109,7 @@ struct time_config_s {
     time_t update_tcp_con; // Refresh network connections
     time_t update_chan_util; // Refresh per radio / SSID channel util info
     time_t update_beacon_reports; // Request BEACON from capable clients
+    time_t client_timeout; // Check for client timeouts.
 };
 
 struct local_config_s {