esp8266/modnetwork.c: Expose configuration for station DHCP hostname.

The ESP SDK supports configuring the hostname that is
reported when doing a DHCP request in station mode.  This commit
exposes that under network.WLAN(network.STA_IF).config('dhcp_hostname')
as a read/write value similar to other parameters.

esp8266/modnetwork.c

@@ -342,6 +342,14 @@ STATIC mp_obj_t esp_config(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs
                         cfg.ap.channel = mp_obj_get_int(kwargs->table[i].value);
                         break;
                     }
+                    case QS(MP_QSTR_dhcp_hostname): {
+                        req_if = STATION_IF;
+                        if (self->if_id == STATION_IF) {
+                            const char *s = mp_obj_str_get_str(kwargs->table[i].value);
+                            wifi_station_set_hostname((char*)s);
+                        }
+                        break;
+                    }
                     default:
                         goto unknown;
                 }
@@ -395,6 +403,12 @@ STATIC mp_obj_t esp_config(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs
             req_if = SOFTAP_IF;
             val = MP_OBJ_NEW_SMALL_INT(cfg.ap.channel);
             break;
+        case QS(MP_QSTR_dhcp_hostname): {
+            req_if = STATION_IF;
+            char* s = wifi_station_get_hostname();
+            val = mp_obj_new_str(s, strlen(s), false);
+            break;
+        }
         default:
             goto unknown;
     }