kernel/posix: passing bad arguments to sys_unlink results in Page Fault in kernel

[badochov]

This simple application results in Page Fault in kernel:

#include <stdio.h>

int main(void)
{
	/* 0x1 to prevent potential NULL checks. */
	sys_unlink(0x1);

	return 0;
}	

Reason:
posix_unlink uses lib_strdup that uses hal_strlen that is the root cause of this problem.
https://github.com/phoenix-rtos/phoenix-rtos-kernel/blob/383558e87fff7ed92f6966449b85ac8f10ac3862/hal/ia32/string.c#L90
hal_strlen doesn't check in any way pointer passed to it and just accesses subsequent bytes until it encounters NUL byte. Moreover passing pathname without NUL byte may also result in pagefault if there is no NUL byte till the end of mapped space.