skbuff.h: Fix comment for NET_IP_ALIGN

Use the correct function call for skb_reserve in the comment for
NET_IP_ALIGN.
Signed-off-by: Tobias Klauser <klto@zhaw.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1342,7 +1342,7 @@ static inline int skb_network_offset(const struct sk_buff *skb)
  * shifting the start of the packet by 2 bytes. Drivers should do this
  * with:
  *
- * skb_reserve(NET_IP_ALIGN);
+ * skb_reserve(skb, NET_IP_ALIGN);
  *
  * The downside to this alignment of the IP header is that the DMA is now
  * unaligned. On some architectures the cost of an unaligned DMA is high