ixgbe: remove simple scalar scattered Rx method

ixgbe: remove simple scalar scattered Rx method

Kill ixgbe_recv_scattered_pkts() - use ixgbe_recv_pkts_lro_single_alloc()
instead.

Work against HW queues in LRO and scattered Rx cases is exactly the same.
Therefore we may drop the inferior callback.

This patch also changes the sw_rsc_ring allocation in the
ixgbe_dev_rx_queue_setup() to always allocate sw_rsc_ring instead of
explicitly allocating it in all possible cases when it may be needed:
LRO and/or scattered Rx.

This will only impose sizeof(void*) * IXGBE_MAX_RING_DESC = 32KB overhead
per Rx queue as a price for a much simpler code, which seems reasonable.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>