use original syscall args in cases when we will do tail_inject

[sivukhin]

• if we will construct syscall from scratch - "unused" args (we have 6 registers in total - but syscall can use less) will be zeroed
• tail_inject will set all registers - potentially overwriting registers unused for this syscall but having some important information for execution
• after this patch I was able to run bash in the sandbox on ARM (with few additional tweaks) - without it shell just behaves "randomly" (it exits immediately, but in some different setups it can work in weird ways - which confirms the explanation of registers overwrite as this will lead to arbitrary UB)

Internally, during tail_inject reverie do:

regs.set_args((
    args.arg0 as Reg,
    args.arg1 as Reg,
    args.arg2 as Reg,
    args.arg3 as Reg,
    args.arg4 as Reg,
    args.arg5 as Reg,
));