Revert "net: correct sk_acceptq_is_full()"

This reverts commit f211ac15.

We had similar attempt in the past, and we reverted it.

History:

64a14651 [NET]: Revert incorrect accept queue backlog changes.
8488df89 [NET]: Fix bugs in "Whether sock accept queue is full" checking

I am adding a fat comment so that future attempts will
be much harder.

Fixes: f211ac15

 ("net: correct sk_acceptq_is_full()")
Cc: iuyacan <yacanliu@163.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>