rewriter: Init only the requested parameters

[xmzzz]

Enable the rewriter initialize only the requested function parameters. After verification by the tools/execsnoop, the result is correct.

For example, In tools/execsnoop, the __envp parameter in the syscall_execve() function is not requested, so it is not initialized.

Before:

...
__attribute__((section(".bpf.fn.syscall__execve")))
int syscall__execve(struct pt_regs *ctx)
{
#if defined(CONFIG_ARCH_HAS_SYSCALL_WRAPPER)
 struct pt_regs * __ctx = (void *)ctx->di;
 const char __user *filename; bpf_probe_read(&filename, sizeof(filename), &__ctx->di);
 const char __user *const __user *__argv; bpf_probe_read(&__argv, sizeof(__argv), &__ctx->si);
 const char __user *const __user *__envp; bpf_probe_read(&__envp, sizeof(__envp), &__ctx->dx);
#else
 const char __user *filename = (const char *)ctx->di; const char __user *const __user *__argv = (const char *const *)ctx->si; const char __user *const __user *__envp = (const char *const *)ctx->dx;
#endif
...

After:

...
__attribute__((section(".bpf.fn.syscall__execve")))
int syscall__execve(struct pt_regs *ctx)
{
#if defined(CONFIG_ARCH_HAS_SYSCALL_WRAPPER)
 struct pt_regs * __ctx = (void *)ctx->di;
 const char __user *filename; bpf_probe_read(&filename, sizeof(filename), &__ctx->di);
 const char __user *const __user *__argv; bpf_probe_read(&__argv, sizeof(__argv), &__ctx->si);
#else
 const char __user *filename = (const char *)ctx->di; const char __user *const __user *__argv = (const char *const *)ctx->si;
#endif
...