net: mvneta: use cache_line_size() to get cacheline size

L1_CACHE_BYTES may not be the real cacheline size, use cache_line_size
to determine the cacheline size in runtime.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Suggested-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>