esp-netif: Support non-lwip mode, add test

It is required to define a mandatory dependency on lwip, so we
introduced esp_netif_stack component and made it require lwip, instead
of directly depending on lwip.
This enables building w-out lwip and support other TCP/IP stacks.

examples/protocols/sntp/main/sntp_example_main.c

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <time.h>
 #include <sys/time.h>
+#include <netdb.h>
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 #include "freertos/event_groups.h"