ixgbe: Use packets to track Tx completions instead of a seperate value

ixgbe: Use packets to track Tx completions instead of a seperate value

A separate value was added to track Tx completions in order to determine if
the Tx unit was hung.  However we can do the same thing using the number of
packets completed without having to add another stat to the Tx ring.

(cherry picked from commit 7d7ce682f8437ff91c964c478b8845ed98a3207d)
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Joe Jin <joe.jin@oracle.com>