ax25: Fix possible oops in ax25_make_new

In ax25_make_new, if kmemdup of digipeat returns an error, there would
be an oops in sk_free while calling sk_destruct, because sk_protinfo
is NULL at the moment; move sk->sk_destruct initialization after this.

BTW of reported-by: Bernard Pidoux F6BVP <f6bvp@free.fr>
Signed-off-by: NJarek Poplawski <jarkao2@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ax25/af_ax25.c

@@ -901,7 +901,6 @@ struct sock *ax25_make_new(struct sock *osk, struct ax25_dev *ax25_dev)
 
 	sock_init_data(NULL, sk);
 
-	sk->sk_destruct = ax25_free_sock;
 	sk->sk_type     = osk->sk_type;
 	sk->sk_priority = osk->sk_priority;
 	sk->sk_protocol = osk->sk_protocol;
@@ -939,6 +938,7 @@ struct sock *ax25_make_new(struct sock *osk, struct ax25_dev *ax25_dev)
 	}
 
 	sk->sk_protinfo = ax25;
+	sk->sk_destruct = ax25_free_sock;
 	ax25->sk    = sk;
 
 	return sk;