esp32/modnetwork: Add max_clients kw-arg to WLAN.config for AP setting.

This allows the user to configure the maximum number of clients that are
connected to the access point.  Resolves #5125.

docs/esp32/quickref.rst

@@ -82,6 +82,7 @@ The :mod:`network` module::
 
     ap = network.WLAN(network.AP_IF) # create access-point interface
     ap.config(essid='ESP-AP') # set the ESSID of the access point
+    ap.config(max_clients=10) # set how many clients can connect to the network
     ap.active(True)         # activate the interface
 
 A useful function for connecting to your local WiFi network is::

ports/esp32/modnetwork.c

@@ -619,6 +619,11 @@ STATIC mp_obj_t esp_config(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs
                         ESP_EXCEPTIONS(tcpip_adapter_set_hostname(self->if_id, s));
                         break;
                     }
+                    case QS(MP_QSTR_max_clients): {
+                        req_if = WIFI_IF_AP;
+                        cfg.ap.max_connection = mp_obj_get_int(kwargs->table[i].value);
+                        break;
+                    }
                     default:
                         goto unknown;
                 }
@@ -693,6 +698,10 @@ STATIC mp_obj_t esp_config(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs
             val = mp_obj_new_str(s, strlen(s));
             break;
         }
+        case QS(MP_QSTR_max_clients): {
+            val = MP_OBJ_NEW_SMALL_INT(cfg.ap.max_connection);
+            break;
+        }
         default:
             goto unknown;
     }