work on linux/armle shellcodes, add source files

Ran into an issue with executing a busybox shell that needs "/bin/sh" in argv[0] to work properly (busybox applet). While looking at the payload module I figured that it currently have the SHELLARG in argv[0] and SHELLARG is limited to 4 bytes (moves through a register).

I reduced the execve part a bit in size (simplified), made a bit more room for SHELLARG, and added the respective source files so that testing is easier.

I did not verify so far whether these still work on the systems they were originally tested on - but they work on the ARM device I'm playing with. The changes are fairly straightforward though.