When the size of the input buffer is not specified, the default was
INT_MAX; however this will cause the pointer value to overflow in many
situations, causing kprint_flush() to flush prematurely and write NUL
bytes at inappropriate places.
This commit changes the default size to 65535. Morale: never use
sprintf() or vsprintf()...
This is based on a port of kprint, which supports standard formats and
options, except for:
* Large parameters (ll)
* Floating-point types (%e, %E, %f, %F, %g, %G, %a, %A)