esp-netif: Added API to get the underlying interface name

The interface name can be used in socket API, i.e. setsockopt(). The API esp_netif_get_netif_impl_name() shoudl be used to populate standard
interface structure struct ifreq.

examples/protocols/sockets/tcp_client_multi_net/main/Kconfig.projbuild

@@ -13,4 +13,12 @@ menu "Example Configuration"
         help
             host port
 
+    config EXAMPLE_BIND_SOCKET_TO_NETIF_NAME
+        bool "Bind to interface by its name"
+        default y
+        help
+            By default example uses setsockopt() to bind the tcp-client's socket
+            to specific interface. Setting this option to true demonstrates binding
+            the socket to the local ip address of the network interface.
+
 endmenu