igb: remove use of skb_dma_map from driver

This change removes skb_dma_map/unmap calls from the igb driver due to the
fact that the call is incompatible with iommu enabled kernels.  In order to
prevent warnings about using the wrong unmap call I have added a
mapped_as_page value to the buffer_info structure to track if the mapped
region is a page or a buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>