Request hostname through DHCP

If hostname is provided, request it to local DNS through DHCP.

Author: guilhermerc

connectivity/lwipstack/source/LWIPInterface.cpp

@@ -433,6 +433,7 @@ LWIP::Interface::Interface() :
 nsapi_error_t LWIP::add_ethernet_interface(EMAC &emac, bool default_if, OnboardNetworkStack::Interface **interface_out, NetworkInterface *user_network_interface)
 {
 #if LWIP_ETHERNET
+    const char *hostname;
     Interface *interface = new (std::nothrow) Interface();
     if (!interface) {
         return NSAPI_ERROR_NO_MEMORY;
@@ -441,6 +442,11 @@ nsapi_error_t LWIP::add_ethernet_interface(EMAC &emac, bool default_if, OnboardN
     interface->memory_manager = &memory_manager;
     interface->ppp_enabled = false;
 
+    hostname = user_network_interface->get_hostname();
+    if (hostname) {
+        netif_set_hostname(&interface->netif, hostname);
+    }
+
 #if (MBED_MAC_ADDRESS_SUM != MBED_MAC_ADDR_INTERFACE)
     netif->interface.hwaddr[0] = MBED_MAC_ADDR_0;
     netif->interface.hwaddr[1] = MBED_MAC_ADDR_1;

connectivity/netsocket/include/netsocket/NetworkInterface.h

@@ -102,7 +102,9 @@ class NetworkInterface: public DNS {
      *  @retval         NSAPI_ERROR_OK on success
      *  @retval         NSAPI_ERROR_UNSUPPORTED if this feature is not supported
      *  @retval         NSAPI_ERROR_PARAMETER if hostname is not valid
-     *  @retval         NSAPI_ERROR_BUSY if hostname couldn't be set
+     *  @retval         NSAPI_ERROR_BUSY if hostname couldn't be set (e.g. for
+     *                  LwIP stack, hostname can only be set before calling
+     *                  \c EthernetInterface::connect method)
      */
     virtual nsapi_error_t set_hostname(const char *hostname);