client-coap.c: Fix client spin loop for NO_SYS == 0

Do not call coap_free_context() from within sigint handler.
Always call coap_io_process().
Use sys_arch_sem_wait() for timeouts while waiting for input.

examples/lwip/client-coap.c

@@ -239,8 +239,6 @@ client_coap_finished(void) {
 
 int
 client_coap_poll(void) {
-#if NO_SYS
   coap_io_process(main_coap_context, 1000);
-#endif /* NO_SYS */
   return quit;
 }

examples/lwip/client.c

@@ -53,9 +53,7 @@ static void
 handle_sigint(int signum) {
   (void)signum;
 
-  client_coap_finished();
-  printf("Client Application finished.\n");
-  exit(0);
+  quit = 1;
 }
 
 /*

examples/lwip/config/lwipopts.h

@@ -10,6 +10,13 @@
  * of use.
  */
 
+/*
+ * NO_SYS = 0
+ *  Use lwIP OS-awareness (multi threaded, semaphores, mutexes and mboxes).
+ *
+ * NO_SYS = 1
+ *  Use lwIP without OS-awareness (no thread, semaphores, mutexes or mboxes).
+ */
 #define NO_SYS                     0
 #define LWIP_SOCKET                (NO_SYS==0)
 #define LWIP_NETCONN               (NO_SYS==0)