test: fix flaky test-net-write-slow

Increase socket timeout so that there is enough time to reliably run the
test on FreeBSD.

Fixes: #7516
PR-URL: #7555
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

test/parallel/test-net-write-slow.js

@@ -12,7 +12,7 @@ buf.fill(0x61); // 'a'
 
 var server = net.createServer(function(socket) {
   socket.setNoDelay();
-  socket.setTimeout(1000);
+  socket.setTimeout(9999);
   socket.on('timeout', function() {
     assert.fail(null, null, 'flushed: ' + flushed +
                 ', received: ' + received + '/' + SIZE * N);