BUG/MEDIUM: stats: stats bind-process doesn't propagate the process mask correctly

With nbproc > 1, it is possible to specify on which process the stats socket
will be bound using "stats bind-process", but the behaviour was not correct,
ignoring the value in some configurations.

Example :
global
  nbproc 4
  stats bind-process 1
  stats socket /var/run/haproxy.sock

With such a configuration, all the processes will listen on the stats socket.
As a workaround, it is also possible to declare a "process" keyword on
the "stats stocket" line.

The patch must be applied to 1.7, 1.6 and 1.5
diff --git a/src/cfgparse.c b/src/cfgparse.c
index dd6f8a2..c55a561 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -8647,7 +8647,7 @@
 		list_for_each_entry(bind_conf, &global.stats_fe->conf.bind, by_fe) {
 			unsigned long mask;
 
-			mask = bind_conf->bind_proc ? bind_conf->bind_proc : nbits(global.nbproc);
+			mask = bind_conf->bind_proc ? bind_conf->bind_proc : 0;
 			global.stats_fe->bind_proc |= mask;
 		}
 		if (!global.stats_fe->bind_proc)