[NET]: Revert incorrect accept queue backlog changes.

This reverts two changes:

8488df89
248f0672

A backlog value of N really does mean allow "N + 1" connections
to queue to a listening socket.  This allows one to specify
"0" as the backlog and still get 1 connection.

Noticed by Gerrit Renker and Rick Jones.

Signed-off-by: David S. Miller <davem@davemloft.net>