net: stmmac: Convert prefetch() to net_prefetch() for received frames

net: stmmac: Convert prefetch() to net_prefetch() for received frames

The size of DMA descriptors is 32 bytes at most.
net_prefetch() for received frames, and keep prefetch() for descriptors.

This patch brings ~4.8% driver performance improvement in a TCP RX
throughput test with iPerf tool on a single isolated Cortex-A65 CPU
core, 2.92 Gbits/sec increased to 3.06 Gbits/sec.

Suggested-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Furong Xu <0x1207@gmail.com>
Reviewed-by: Yanteng Si <si.yanteng@linux.dev>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>