e1000e: commonize tx cleanup routine to match e1000 & igb

This change updates the e1000e tx cleanup routine to more closely match
what already exists in igb and e1000.

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>