ixgbe: Remove code that was initializing Rx page offset

This change reverts an earlier patch that introduced
ixgbe_init_rx_page_offset. The idea behind the function was to provide
some variation in the starting offset for the page in order to reduce
hot-spots in the cache. However it doesn't appear to provide any
significant benefit in the testing I have done. It has however been a
source of several bugs, and it blocks us from being able to use 2K
fragments on larger page sizes. So the decision I made was to remove it.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>