appletalk: Set skb with destructor

The sock ref counting is off so there is a kernel panic when you run
`atalkd`.  See https://bugzilla.kernel.org/show_bug.cgi?id=79441
This fix is similar to 0ae89beb283a ('can: add destructor for self
generated skbs')

Reported-by: Ed Martin <edman007@edman007.com>
Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>