Merge branch 'bugfix/netif_zero_init' into 'master'

Zero-fill netif on alloc

LwIP's `struct netif` was not zero-initialized after allocation, so `ipv6_addr_cb ` function pointer contained garbage. This caused a crash if the device was on an IPv6 capable network.

Fixes https://github.com/espressif/esp-idf/issues/133, https://github.com/espressif/esp-idf/issues/147, https://github.com/espressif/esp-idf/issues/142.

Source: https://github.com/espressif/esp-idf/pull/148

See merge request !289

components/tcpip_adapter/tcpip_adapter_lwip.c

@@ -64,7 +64,7 @@ esp_err_t tcpip_adapter_start(tcpip_adapter_if_t tcpip_if, uint8_t *mac, tcpip_a
     }
 
     if (esp_netif[tcpip_if] == NULL) {
-        esp_netif[tcpip_if] = malloc(sizeof(struct netif));
+        esp_netif[tcpip_if] = calloc(1, sizeof(*esp_netif[tcpip_if]));
         if (esp_netif[tcpip_if] == NULL) {
             return ESP_ERR_NO_MEM;
         }