Fixing changes to make greentea test mbed-os-tests-netsocket-connectivity pass for target Realtek AMEBA

Author: prashantrar

features/FEATURE_LWIP/lwip-interface/lwip_stack.c

@@ -594,11 +594,13 @@ nsapi_error_t mbed_lwip_emac_init(emac_interface_t *emac)
 // Backwards compatibility with people using DEVICE_EMAC
 nsapi_error_t mbed_lwip_init(emac_interface_t *emac)
 {
-    nsapi_error_t ret;
+    nsapi_error_t ret = NSAPI_ERROR_OK;
     mbed_lwip_core_init();
-    ret = mbed_lwip_emac_init(emac);
-    if (ret == NSAPI_ERROR_OK) {
-        netif_inited = true;
+    if(netif_inited == false){
+        ret = mbed_lwip_emac_init(emac);
+        if (ret == NSAPI_ERROR_OK) {
+            netif_inited = true;
+        }
     }
     return ret;
 }

targets/TARGET_Realtek/TARGET_AMEBA/RTWInterface.cpp

@@ -228,8 +228,9 @@ nsapi_error_t RTWInterface::connect(const char *ssid, const char *pass,
 nsapi_error_t RTWInterface::disconnect()
 {
     char essid[33];
-
+	
     wlan_emac_link_change(false);
+	mbed_lwip_bringdown();
     if(wifi_is_connected_to_ap() != RTW_SUCCESS)
         return NSAPI_ERROR_NO_CONNECTION;
     if(wifi_disconnect()<0){