BUG/MINOR: systemd: ignore daemon mode

Since we switched to notify mode in the systemd unit file in commit
d6942c8, haproxy won't start if the daemon keyword is present in the
configuration.

This change makes sure that haproxy remains in foreground when using
systemd mode and adds a note in the documentation.

doc/configuration.txt

@@ -680,7 +680,8 @@ crt-base <dir>
 daemon
   Makes the process fork into background. This is the recommended mode of
   operation. It is equivalent to the command line "-D" argument. It can be
-  disabled by the command line "-db" argument.
+  disabled by the command line "-db" argument. This option is ignored in
+  systemd mode.
 
 deviceatlas-json-file <path>
   Sets the path of the DeviceAtlas JSON data file to be loaded by the API.

src/haproxy.c

@@ -1363,7 +1363,7 @@ static void init(int argc, char **argv)
 			else if (*flag == 'D')
 				arg_mode |= MODE_DAEMON;
 			else if (*flag == 'W' && flag[1] == 's') {
-				arg_mode |= MODE_MWORKER;
+				arg_mode |= MODE_MWORKER | MODE_FOREGROUND;
 #if defined(USE_SYSTEMD)
 				global.tune.options |= GTUNE_USE_SYSTEMD;
 #else