WEP connection issue

### Basic Infos

- [x] This issue complies with the [issue POLICY doc](https://github.com/esp8266/Arduino/blob/master/POLICY.md).
- [x] I have read the documentation at [readthedocs](https://arduino-esp8266.readthedocs.io/en/latest) and the issue is not addressed there.
- [x] I have tested that the issue is present in current master branch (aka latest git).
- [x] I have searched the issue tracker for a similar issue.
- [x] If there is a stack dump, I have decoded it.
- [x] I have filled out all fields below.

#### Platform

- Hardware: [ESP-8266 NodeMCU v3]
- Core Version: [latest git hash or date]
- Development Env: [Arduino IDE]
- Operating System: [Ubuntu]

### Settings in IDE

- Module: [Nodemcu]
- Flash Mode: [?]
- Flash Size: [4MB]
- lwip Variant: [?]
- Reset Method: [nodemcu]
- Flash Frequency: [40Mhz]
- CPU Frequency: [80Mhz]
- Upload Using: [SERIAL]
- Upload Speed: [115200]

### Problem Description

I cannot get the ESP8266 module to connect to a WEP SSID. The sketch below is what I am using. The module will try connecting, and then give the following output:
```
WiFi connected
IP address:
169.254.215.189
```

All subsequent attempts also yield a 169.154.X.X address. The module is also not visible in the DHCP leases overview of the AP.

Am I missing something here?

### [MCVE](https://stackoverflow.com/help/mcve) Sketch

```cpp

// Libraries
#include

// WiFi network
const char* ssid = "SSID_NAME";
const char* password = "PASSWORD";

void setup() {

// Enable WEP
WiFi.enableInsecureWEP();

// Start serial
Serial.begin(115200);
delay(10);

// Connecting to a WiFi network
Serial.println();
Serial.println();
Serial.print("Connecting to ");
Serial.println(ssid);

WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}

Serial.println("");
Serial.println("WiFi connected");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
}

void loop() {

}
```

Beginne mit der MCVE-Skizze, insbesondere WiFi.enableInsecureWEP(), WiFi.begin() und der WL_CONNECTED-Schleife, und reproduziere sie auf dem aufgeführten ESP8266 NodeMCU v3-Setup mit einer WEP-SSID. Untersuche, warum die Verbindung Erfolg meldet, während sie eine 169.254.x.x-Adresse erhält und in den DHCP-Leases des AP fehlt; als abgeschlossen gilt die Aufgabe, wenn die Ursache identifiziert und das daraus resultierende Verbindungsverhalten dokumentiert oder korrigiert wurde.

Vom Indexierungsmodell aus dem Issue-Text verfasst.