net/sfc: avoid usage of prepared packets number in EF10 Rx
net/sfc: avoid usage of prepared packets number in EF10 Rx

Number of prepared packets is good when one Rx descriptor is one packet.
Introduce pending Rx descriptor pointer which points to the first not
processed Rx descriptors. Rx descriptors from completed to pending have
buffers ready to be passed to application.

Signed-off-by: Andrew Rybchenko <ac94ab2a8fe9a9a087f6e24dcbc16626b52c07e8@solarflare.com>
Reviewed-by: Ivan Malov <436a2feb05eb79a6862681e66bd0193220e8fb2d@oktetlabs.ru>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk