net/sfc/base: import MAC statistics

net/sfc/base: import MAC statistics

MAC statistics are either periodically (if supported/requested)
or on-demand written to provided DMA-mapped memory.
If periodic update is not supported (e.g. for EF10 virtual
functions), it is the driver responsibility to handle it.

EFSYS_OPT_MAC_STATS should be enabled to use it.

From Solarflare Communications Inc.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>