igb: fix panic while dumping packets on Tx hang with IOMMU

This patch resolves a "BUG: unable to handle kernel paging request at ..."
oops while dumping packet data. The issue occurs with IOMMU enabled due to
the address provided by phys_to_virt().

This patch avoids phys_to_virt() by making using skb->data and the address
of the pages allocated for Rx.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>