QSslSocket: improve documentation of the supported protocols

1) To describe a protocol version we should use an "ordinary" name,
not use the values out of the QSsl::SslProtocol enum.

2) Say that we support the latest stable TLS version (1.2, not 1.0).

3) Fix a statement about which protocol is the default one.

Change-Id: I18732914d55060a0c3920f7082f986c262a71ded
Reviewed-by: André Klitzing <aklitzing@gmail.com>
Reviewed-by: Richard J. Moore <rich@kde.org>

src/network/ssl/qsslsocket.cpp

@@ -49,7 +49,8 @@
     QSslSocket establishes a secure, encrypted TCP connection you can
     use for transmitting encrypted data. It can operate in both client
     and server mode, and it supports modern SSL protocols, including
-    SSLv3 and TLSv1_0. By default, QSslSocket uses TLSv1_0, but you can
+    SSL 3 and TLS 1.2. By default, QSslSocket uses only SSL protocols
+    which are considered to be secure (QSsl::SecureProtocols), but you can
     change the SSL protocol by calling setProtocol() as long as you do
     it before the handshake has started.