Add functions to change kernel log level dynamically

printk.c

// kernel/kernel/printk.c

static int kmsg_level = 0;

void set_kmsg_lebel(int level)
{
    kmsg_level = level;
}

void kmsg_write(const char *fmt, ...)
{
    va_list args;
    if (kmsg_level != 0) {
        va_start(args, fmt);
        vprintk(fmt, args);
        va_end(args);
    }
}

printk.h

// kernel/include/linux/printk.h

extern void set_kmsg_lebel(int level);
extern void kmsg_write(const char *fmt, ...);