r8169: Avoid memcpy() over-reading of ETH_SS_STATS

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally reading across neighboring array fields.

The memcpy() is copying the entire structure, not just the first array.
Adjust the source argument so the compiler can do appropriate bounds
checking.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>