executor: kMaxArgs > 10 behaves weirdly

[israelsucks]

Describe the bug
To fuzz an interface defined as a pseudo syscall which expect 11 arguments, I've increased the related maxArgs fields in both executor.cc and prog/types.go. However, for some unknown reason, the 11th argument becomes a pointer to the syscall name ("syz_my_target_iface").

To Reproduce
Define a bogus pseudo syscall with 11 arguments. Then do the following in it:

	char buf[100];
	memcpy(buf, (int*)arg11, 100);
	printf("11th argument: 0x%lx points to: %s\n", arg11, buf);

Then call it e.g ./syz-execprog -debug -threaded=0 mytest

Expected behavior
kMaxArgs of executor.cc and maxArgs of prog/types.go should have been enough to alter the max args support.

Regards