dhcp_discover: add hostname option

ref: esp8266/Arduino#8247

Author: d-a-v

glue-lwip/arduino/lwipopts.h

@@ -3592,8 +3592,13 @@ extern void lwip_hook_dhcp_parse_option(struct netif *netif, struct dhcp *dhcp,
                                         int option_value_offset);
 
 #if LWIP_FEATURES
-#define LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, state, msg, msg_type, option_len_ptr) \
-   lwip_hook_dhcp_amend_options(netif, dhcp, state, msg, msg_type, option_len_ptr)
+#define LWIP_HOOK_DHCP_APPEND_OPTIONS(netif, dhcp, state, msg, msg_type, option_len_ptr) { \
+   /* https://github.com/esp8266/Arduino/issues/8223 */ \
+   lwip_hook_dhcp_amend_options(netif, dhcp, state, msg, msg_type, option_len_ptr); \
+   /* https://github.com/esp8266/Arduino/issues/8247 */ \
+   if ((msg_type) == DHCP_DISCOVER) \
+      *(option_len_ptr) = dhcp_option_hostname(*(option_len_ptr), (msg)->options, netif); \
+}
 
 extern void lwip_hook_dhcp_amend_options(struct netif *netif, struct dhcp *dhcp, int state, struct dhcp_msg *msg,
                                          int msg_type, u16 *option_len_ptr);