BUG/MINOR: listener: stop unbound listeners on startup

BUG/MINOR: listener: stop unbound listeners on startup

When a listener is not bound to a process its frontend belongs to, it
is only paused and not stopped. This creates confusion from the outside
as "netstat -ltnp" for example will report only the parent process as
the listener instead of the effective one. "ss -lnp" will report that
all processes are listening to all sockets.

This is confusing enough to suggest a fix. Now we simply stop the unused
listeners. Example with this simple config :

  global
      nbproc 4

  frontend haproxy_test
      bind-process 1-40
      bind :12345 process 1
      bind :12345 process 2
      bind :12345 process 3
      bind :12345 process 4

Before the patch :
  $ netstat -ltnp
  Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30457/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30457/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30457/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30457/./haproxy

After the patch :
  $ netstat -ltnp
  Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30504/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30503/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30502/./haproxy
  tcp        0      0 0.0.0.0:12345           0.0.0.0:*               LISTEN      30501/./haproxy

This patch may be backported to 1.6 and 1.5, but it relies on commit
7a798e5 ("CLEANUP: fix inconsistency between fd->iocb, proto->accept
and accept()") since it will expose an API inconsistency by including
listener.h in the .c.