Copy ioperm bitmaps more efficiently at context switch time.  Only copy
upto the highest used port.

Originally from Ingo Molnar
Signed-off-by: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>