ixgbe: Move all values that deal with count, next_to_use, next_to_clean to u16

ixgbe: Move all values that deal with count, next_to_use, next_to_clean to u16

This change updates all values dealing with count, next_to_use, and
next_to_clean so that they stay u16 values.  The advantage of this is that
there is no re-casting of type during the propagation through the stack.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 63544e9c0055316d0397cb671f2ff99d85c77293)

Signed-off-by: Joe Jin <joe.jin@oracle.com>