D-Link UPnP M-Search Command Injection

This is the Metasploit module for the command injection detected and exploited by Zachary Cutlip:
http://shadow-file.blogspot.de/2013/02/dlink-dir-815-upnp-command-injection.html
https://github.com/zcutlip/exploit-poc/tree/master/dlink/dir-815-a1/upnp-command-injection

Tested on my DIR-300, DIR-645. Zach has reported the DIR-815 and there are a ton of devices with the same codebase out there ;)

![dlink_msearch_echo](https://cloud.githubusercontent.com/assets/497520/3292774/18df6b74-f593-11e3-9a09-2c91ea99d618.png)

Please, have into account the recent changes to the CmdStager mixin after #2484. YARD documentation has been added to the mixin. Also, every module using CmdStager in master has been updated. So it's full of samples. If there are doubts still about how to use the CmdStager after #2484, feel free to ask! Thanks!