e1000e: Fix jumbo frame receive code.

Fix allocation and freeing of jumbo frames where several bugs
were recently introduced by cleanups after we forked this code
from e1000. This moves ps_pages to buffer_info where it really
belongs and makes it a dynamically allocated array. The penalty
is not that high since it's allocated outside of the buffer_info
struct anyway.

Without this patch all jumbo frames are completely broken and the
driver panics.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>