e1000: fix tx hang detect logic and address dma mapping issues

This patch changes the dma mapping to better support
skb_dma_map/skb_dma_unmap and addresses and redefines the tx hang logic to
be based off of time stamp instead of if the dma field is populated

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>