esp32,esp8266: Rename WLAN dhcp_hostname config to hostname.

But retain old name for backwards compatibility.

docs/library/network.WLAN.rst

@@ -130,7 +130,7 @@ Methods
    hidden         Whether SSID is hidden (boolean)
    security       Security protocol supported (enumeration, see module constants)
    key            Access key (string)
-   dhcp_hostname  The DHCP hostname to use
+   hostname       The hostname that will be sent to DHCP (STA interfaces) and mDNS (if supported, both STA and AP)
    reconnects     Number of reconnect attempts to make (integer, 0=none, -1=unlimited)
    txpower        Maximum transmit power in dBm (integer or float)
    =============  ===========

ports/esp32/network_wlan.c

@@ -452,6 +452,7 @@ STATIC mp_obj_t network_wlan_config(size_t n_args, const mp_obj_t *args, mp_map_
                         cfg.ap.channel = mp_obj_get_int(kwargs->table[i].value);
                         break;
                     }
+                    case MP_QSTR_hostname:
                     case MP_QSTR_dhcp_hostname: {
                         const char *s = mp_obj_str_get_str(kwargs->table[i].value);
                         esp_exceptions(tcpip_adapter_set_hostname(self->if_id, s));
@@ -538,6 +539,7 @@ STATIC mp_obj_t network_wlan_config(size_t n_args, const mp_obj_t *args, mp_map_
             req_if = WIFI_IF_AP;
             val = MP_OBJ_NEW_SMALL_INT(cfg.ap.channel);
             break;
+        case MP_QSTR_hostname:
         case MP_QSTR_dhcp_hostname: {
             const char *s;
             esp_exceptions(tcpip_adapter_get_hostname(self->if_id, &s));

ports/esp8266/modnetwork.c

@@ -397,6 +397,7 @@ 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 MP_QSTR_hostname:
                     case MP_QSTR_dhcp_hostname: {
                         req_if = STATION_IF;
                         if (self->if_id == STATION_IF) {
@@ -461,6 +462,7 @@ 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 MP_QSTR_hostname:
         case MP_QSTR_dhcp_hostname: {
             req_if = STATION_IF;
             char *s = wifi_station_get_hostname();