Enable more than 4 clients for the Range-Extender (Including proposed changes to the code)

[qc-1998]

I really like the Range Extender feature.
It is useful to be able to use a 5$ ESP32 dev-board instead of a full-blown Wi-Fi Access Point to solve Wi-Fi reception and/or range issues.

After trying to use an 'Extender' ESP32 to cover an area with 5-6 devices, I was surprised to discover that the Extender is limited to just 4 WiFi clients.
(I did not see that mentioned in the Docs - I discovered it by going over the Extender driver source code)
Apparently, the softAP() function limits the number of Wi-Fi clients / connections to 4 by default:

//
bool softAP(const char* ssid, const char* passphrase = NULL, int channel = 1, int ssid_hidden = 0, int max_connection = 4);
//

From what I understand, the ESP SDK is (hard?) limited to a maximum of 10.

I think that it would be beneficial to be able to set a different connection limit (up to 10) at compile time.
I compiled a custom test version with a 10 client limit, and it seems to run well.
(See below example with 6 clients connected - tested on a dev-board with ESP32-D0WDQ6):

19:07:37.128 MQT: stat/EXTENDER_GARAGE/RESULT = {"RgxClients":{
"D8F15BDB3942":{"IPAddress":"192.168.243.2","RSSI":-42},
"ECDA3B368184":{"IPAddress":"192.168.243.3","RSSI":-64},
"083AF2453284":{"IPAddress":"192.168.243.9","RSSI":-80},
"24A160303D5B":{"IPAddress":"192.168.243.7","RSSI":-56},
"E8DB849D4795":{"IPAddress":"192.168.243.10","RSSI":-40},
"2CF432E52692":{"IPAddress":"192.168.243.11","RSSI":-56}}
}

Below are the (minor) changes I made to make it work:

Tasmota/tasmota/tasmota_xdrv_driver/xdrv_58_range_extender.ino:

  WiFi.softAPConfig(Settings->ipv4_rgx_address, Settings->ipv4_rgx_address, Settings->ipv4_rgx_subnetmask);

// Begin Modification

  //Set Extender MAX Clients
  int max_clients = 4;
#ifdef WIFI_RANGE_EXTENDER_MAX_CLIENTS
  max_clients = WIFI_RANGE_EXTENDER_MAX_CLIENTS;
#endif
  //bool softAP(const char* ssid, const char* passphrase = NULL, int channel = 1, int ssid_hidden = 0, int max_connection = 4);
  //WiFi.softAP(SettingsText(SET_RGX_SSID), SettingsText(SET_RGX_PASSWORD));  
  WiFi.softAP(SettingsText(SET_RGX_SSID), SettingsText(SET_RGX_PASSWORD), 0, 0, max_clients);
  AddLog(LOG_LEVEL_INFO, PSTR("RGX: WiFi Extender AP Enabled with SSID: %s, Max Clients: %d"), WiFi.softAPSSID().c_str(),max_clients);

//End Modification

user_config_override.h:

#define USE_WIFI_RANGE_EXTENDER
#define USE_WIFI_RANGE_EXTENDER_NAPT
#define WIFI_RANGE_EXTENDER_MAX_CLIENTS 10

These changes allow you to define WIFI_RANGE_EXTENDER_MAX_CLIENTS at compile time, with valid values of 1-10.
If it is not defined, then the previous limit of 4 is used.
Another change is that the maximum number of clients is printed to the log, so the user would be made aware of it.

The changes leave the default behavior unchanged, and thus I think it is relatively 'low-risk' to add this to the code base.

Beside the suggested changes to xdrv_58_range_extender.ino, I think that the max client limitation should be better documented in docs/Range-Extender.md.

I hope someone finds this useful, and that this could be added to the main codebase at some point. :-)