syslogd.service: use journald socket, not /dev/log

This patch fixes integration with systemd-journald, and also sets the
now mandatory KillMode.

When running on systems with systemd-journald certain considerations
must be taken.  These are listed here:

  https://www.freedesktop.org/wiki/Software/systemd/syslog/

In it simplest form, the system as a whole logs through journald and
a BSD syslog daemon then gets its log messages from journald.

NOTE: due to issues with the Debian packaging of rsyslog, the sysklogd
      packages cannot be used to replace rsyslog.  First rsyslog must
      be purged to clear the syslog.socket symlink, then sysklogd can
      be installed.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

debian/changelog

@@ -1,3 +1,11 @@
+sysklogd (2.3.0) stable; urgency=medium
+
+  * PREVIEW BUILD
+  * Use systemd KillMode=process
+  * Let syslogd use another socket when journald is active (systemd systems)
+
+ -- Joachim Wiberg <troglobit@gmail.com>  Wed, 23 Jun 2021 15:24:00 +0200
+
 sysklogd (2.2.3) stable; urgency=medium
 
   * Fix problem with log messages stuck in 1969.  When not using libsyslog,

syslogd.service.in

@@ -6,9 +6,10 @@ Requires=syslog.socket
 
 [Service]
 EnvironmentFile=-@SYSCONFDIR@/default/syslogd
-ExecStart=@SBINDIR@/syslogd -F $SYSLOGD_OPTS
+ExecStart=@SBINDIR@/syslogd -F -p /run/systemd/journal/syslog $SYSLOGD_OPTS
 StandardOutput=null
 Restart=on-failure
+KillMode=process
 
 [Install]
 WantedBy=multi-user.target