e1000e: Re-enable SECRC - crc stripping

This workaround code performed software stripping instead of the
hardware which can do it much faster. None of the e1000e target
hardware has issues with this feature and should work fine. This
gives us some performance back on receive, and removes some
kludging stripping the 4 bytes.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>