ipv6: fix the comment of ip6_xmit()

ip6_xmit() is used by upper transport protocol.
Signed-off-by: NShan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -181,7 +181,7 @@ int ip6_output(struct sk_buff *skb)
 }
 
 /*
- *	xmit an sk_buff (used by TCP)
+ *	xmit an sk_buff (used by TCP, SCTP and DCCP)
  */
 
 int ip6_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl,