SSLSocket is not closed when disconnected from the broker

Hi,
Our project uses the paho in the unstable network conditions. We sometimes get the broker unreachable for a few minutes.
If the broker is unreachable for a long time, the connection to the broker is closed when the keepAliveInterval timeout expires, but the underlying socket is not closed if it is SSLSocket.

In `TCPNetworkModule#stop`, `shutdownInput` is called before `close`. However, if the socket is a SSLSocket, `close` is never called since `shutdownInput` always throws `UnsupportedOperationException`.
```
public void stop() throws IOException {
if (socket != null) {
// CDA: an attempt is made to stop the receiver cleanly before closing the socket.
...
// want to move it in SSLNetworkModule.

socket.shutdownInput();
socket.close();
}
```

The netstat log shows that the old tcp connection is still alive even after the reconnect cycle has begun.
```
pi@8e65eabebd90:~/work$ netstat -ant
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp6 0 11479 172.17.0.2:46858 184.172.124.189:8883 ESTABLISHED
tcp6 0 1 172.17.0.2:46860 184.172.124.189:8883 SYN_SENT
```

- [x] Bug exists Release Version 1.2.0 ( Master Branch)
- [x] Bug exists in Snapshot Version 1.2.1-SNAPSHOT (Develop Branch)
- [?] Bug exists in MQTTv5 Version (mqttv5-new Branch)