ipv6: remove obsolete comment in ip6_append_data()

After 11878b40e[net-timestamp: SOCK_RAW and PING timestamping], this comment
becomes obsolete since the codes check not only UDP socket, but also RAW sock;
and the codes are clear, not need the comments

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -1270,7 +1270,6 @@ emsgsize:
 		}
 	}
 
-	/* For UDP, check if TX timestamp is enabled */
 	if (sk->sk_type == SOCK_DGRAM || sk->sk_type == SOCK_RAW)
 		sock_tx_timestamp(sk, &tx_flags);