MXS-2486: Move to_string into SSLProvider

The functionality is more a part of the provider than the context so it
should be defined in it. It also doesn't use any parts of the SSLContext
which makes it somewhat more clear that it doesn't belong there.

include/maxscale/ssl.hh

@@ -117,12 +117,6 @@ public:
         return m_cfg;
     }
 
-    // Convert to JSON representation
-    json_t* to_json() const;
-
-    // Convert to human readable string representation
-    std::string to_string() const;
-
     ~SSLContext();
 
 private:
@@ -144,12 +138,21 @@ public:
 
     SSLProvider(std::unique_ptr<mxs::SSLContext> context);
 
+    // Return true if SSL is enabled
+    bool enabled() const
+    {
+        return m_context.get();
+    }
+
     // Current configuration
     const mxs::SSLConfig& config() const;
 
     // The context or nullptr if no context is set
     mxs::SSLContext* context() const;
 
+    // Convert to human readable string representation
+    std::string to_string() const;
+
     // Set the context, argument must not be null
     void set_context(std::unique_ptr<mxs::SSLContext> ssl);