Make use of the iptables conntrack module instead of the older state module
for stateful firewalling.

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
(Backported commit f22b7bb5529b816eef840a1180b677e4ea31b124)

The eurephia plug-in would daemonize the OpenVPN process by calling
daemonize() too early.  This patch renames daemoinze() to efw_daemonize()
and calls it only in the firewall child process.

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
(cherry picked from commit 525d75316848f79208101e48a54e21396464c98b)

The memory leak was caused by not freeing the shadow context the firewall
child process uses for logging.  In addition this child process had a
connection to the database open as well, which was not needed.  This
connection is now disconnected immediately after the child process has
started.

Added also usage of mlock() to protect sensitive information from being
swapped out to disk.

This only affects functions related to MAC address and certificate depth

Also simplified the initialisation of the logging module.  By calling
the eurephia_log_init(eurephiaCTX *, char *dest, int loglevel) function,
a log context will be setup inside the eurephiaCTX.

To close the log file, eurephia_log_close(eurephiaCTX *) must be called.

The destination string to eurephia_log_init() can be:

	- stdout:
	  Log everything to stdout
	- stderr:
	  Log everything to stderr
	- none:
	  Do no logging at all
	- syslog:<facility>
	  Log via syslog.  <facility> can be: user, local[0-7],
	  daemon or authpriv.
	- Filename
	  All logging goes to the given filename.  If the filename
	  string is not recognised by any of the reserved words above,
	  it will be handled as a filename.

This also improves debugging as well, if debug logging is enabled and log level is >= 40.