add ENABLE_FEATURE_SYSTEMD and use it in syslogd

Signed-off-by: Davide Cavalca <davide@geexbox.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

sysklogd/syslogd.c

@@ -512,6 +512,11 @@ static NOINLINE int create_socket(void)
 	int sock_fd;
 	char *dev_log_name;
 
+#if ENABLE_FEATURE_SYSTEMD
+	if (sd_listen_fds() == 1)
+		return SD_LISTEN_FDS_START;
+#endif
+
 	memset(&sunx, 0, sizeof(sunx));
 	sunx.sun_family = AF_UNIX;