atm: use SKB_TRUESIZE() in atm_guess_pdu2truesize()

SKB_TRUESIZE() provides a better approximation of expected skb truesize.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/atmdev.h

@@ -452,7 +452,7 @@ void atm_dev_release_vccs(struct atm_dev *dev);
 
 static inline int atm_guess_pdu2truesize(int size)
 {
-	return SKB_DATA_ALIGN(size) + sizeof(struct skb_shared_info);
+	return SKB_TRUESIZE(size);
 }