ixgbe: fix scalar scattered Rx with CRC

For 2.1 release, in attempt to minimize number of RX routines to support,
ixgbe scatter and ixgbe LRO RX routines were merged into one
that can handle both cases.
Though I completely missed the fact, that while LRO could only be used
when HW CRC strip is enabled, scatter RX should work for both cases
(HW CRC strip on/off).
That patch restores missed functionality.

Fixes: 9d8a92628f21 ("ixgbe: remove simple scalar scattered Rx method")

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Wenzhuo Lu <wenzhuo.lu@intel.com>