appletalk: Fix socket referencing in skb

Setting just skb->sk without taking its reference and setting a
destructor is invalid. However, in the places where this was done, skb
is used in a way not requiring skb->sk setting. So dropping the setting
of skb->sk.
Thanks to Eric Dumazet <eric.dumazet@gmail.com> for correct solution.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=79441


Reported-by: Ed Martin <edman007@edman007.com>
Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>