e1000e: use either_crc_le() rather than re-write it

For the 82579 jumbo frame workaround, there is no need to re-write the CRC
calculation functionality already found in the kernel's ether_crc_le().

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>