add a robust reverse_tcp shellcode for mipsbe

[cq674350529]

Currently, the reverse_tcp shellcode for mipsbe contains some bad chars like '\x00', which won't work in http requests. I have developed a more robust shellcode and tested it on some real devices. The shellcode avoid some common bad chars ('\x00', '\x20', '\x23', '\x0d\x0a'), and the link on exploit-db is: https://www.exploit-db.com/shellcodes/45541 .

So is it acceptable to add a new mipsbe reverse_tcp shellcode? If yes, replace the original one directly or add a new file called reverse_tcp_xxx.py?

Thanks!

Steps to Reproduce (for bugs)

Your Environment

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• Operating System and version:
• Python Version: ( python3 --version )
• Python Environment: ( python3 -m pip freeze )

Current Behavior

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Expected Behavior

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