r8169: fix kasan reported skb use-after-free.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Fixes: d7d2d89d ("r8169: Add software counter for multicast packages")
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Corinna Vinschen <vinschen@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>