shutdown(2) should not be called for SSLSocket.

SSLSocket#stop is a private method and cannot be called, but explicit calls
are not necessary because SSL_shutdown() is called from SSLSocket#close.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56846 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/net/ftp.rb

@@ -1406,11 +1406,13 @@ module Net
       end
 
       def shutdown(*args)
-        if @io.respond_to?(:stop)
-          # shut down the TLS connection gracefully.
-          @io.stop
+        if defined?(OpenSSL::SSL::SSLSocket) &&
+            @io.is_a?(OpenSSL::SSL::SSLSocket)
+          # If @io is an SSLSocket, SSL_shutdown() will be called from
+          # SSLSocket#close, so shutdown(2) should not be called.
+        else
+          @io.shutdown(*args)
         end
-        @io.to_io.shutdown(*args)
       end
 
       def read(len = nil)