net: document skb parameter in function 'skb_gso_size_check'

Remove kernel-doc warning:

  net/core/skbuff.c:4953: warning: Function parameter or member 'skb' not described in 'skb_gso_size_check'
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -4944,6 +4944,8 @@ static unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
  *
  * This is a helper to do that correctly considering GSO_BY_FRAGS.
  *
+ * @skb: GSO skb
+ *
  * @seg_len: The segmented length (from skb_gso_*_seglen). In the
  *           GSO_BY_FRAGS case this will be [header sizes + GSO_BY_FRAGS].
  *