tls: fix premature connection termination

Destroying the TLS session implies destroying the underlying socket but
before this commit, that was done with net.Socket#destroy() rather than
net.Socket#destroySoon().  The former closes the connection right away,
even when there is still data to write.  In other words, sometimes the
final TLS record got truncated.

Fixes #6107.

lib/tls.js

@@ -1400,7 +1400,7 @@ function pipe(pair, socket) {
       // Encrypted should be unpiped from socket to prevent possible
       // write after destroy.
       pair.encrypted.unpipe(socket);
-      socket.destroy();
+      socket.destroySoon();
     });
   });