net/ice/base: enable HW to prefetch Rx descriptors

net/ice/base: enable HW to prefetch Rx descriptors

Currently we are always setting prefena to 0. This is causing the
hardware to only fetch descriptors when there are none free in the cache
for a received packet instead of prefetching when it has used the last
descriptor regardless of incoming packets.

Fix this by allowing the hardware to prefetch Rx descriptors.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>
Signed-off-by: Leyi Rong <leyi.rong@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>