[Patch]Add a function kernel_string2 for copy non-0-terminated string with fixed length from kernel space at given address.

[Stone, Joshua I]

Cai Fei wrote:
> So I added a function kernel_string2 for copy non-0-terminated string
> with fixed length from kernel space at given address. Also, the man
> paged is updated.

The new function looks fine.  My only suggestion is that a more
meaningful name would be nice.  Maybe kernel_string_n or
kernel_string_max.

Oh, tests would also be nice.

Thanks,

Josh