net: remove a stale comment for dl_next

dl_next member in struct request_sock doesn't need to be first.

We expect to insert a "struct common_sock" or a subset of it,
so this claim had to be verified.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/request_sock.h

@@ -48,7 +48,7 @@ extern int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req);
 /* struct request_sock - mini sock to represent a connection request
  */
 struct request_sock {
-	struct request_sock		*dl_next; /* Must be first member! */
+	struct request_sock		*dl_next;
 	u16				mss;
 	u8				num_retrans; /* number of retransmits */
 	u8				cookie_ts:1; /* syncookie: encode tcpopts in timestamp */