DOC: fix proxy protocol v2 decoder example

Richard Russo reported that the example code in the PP spec is wrong
now that we slightly changed the format to merge <ver> and <cmd>. Also
rename the field <ver_cmd> to avoid any ambiguity on the usage.
BUG/MEDIUM: Fix unhandled connections problem with systemd daemon mode and SO_REUSEPORT.

Using the systemd daemon mode the parent doesn't exits but waits for
his childs without closing its listening sockets.

As linux 3.9 introduced a SO_REUSEPORT option (always enabled in
haproxy if available) this will give unhandled connections problems
after an haproxy reload with open connections.

The problem is that when on reload a new parent is started (-Ds
$oldchildspids), in haproxy.c main there's a call to start_proxies
that, without SO_REUSEPORT, should fail (as the old processes are
already listening) and so a SIGTOU is sent to old processes. On this
signal the old childs will call (in pause_listener) a shutdown() on
the listening fd. From my tests (if I understand it correctly) this
affects the in kernel file (so the listen is really disabled for all
the processes, also the parent).

Instead, with SO_REUSEPORT, the call to start_proxies doesn't fail and
so SIGTOU is never sent. Only SIGUSR1 is sent and the listen isn't
disabled for the parent but only the childs will stop listening (with
a call to close())

So, with SO_REUSEPORT, the old childs will close their listening
sockets but will wait for the current connections to finish or
timeout, and, as their parent has its listening socket open, the
kernel will schedule some connections on it. These connections will
never be accepted by the parent as it's in the waitpid loop.

This fix will close all the listeners on the parent before entering the
waitpid loop.

Signed-off-by: Simone Gotti <simone.gotti@gmail.com>