ipsec: reintroduce IPsec support for tunneling

This patch reintroduces ovs-monitor-ipsec daemon that
was previously removed by commit 2b02d770 ("openvswitch:
Allow external IPsec tunnel management.")

After this patch, there are no IPsec flavored tunnels anymore.
IPsec is enabled by setting up the right values in:
1. OVSDB:Interface:options column;
2. OVSDB:Open_vSwitch:other_config column;
3. OpenFlow pipeline.

GRE, VXLAN, GENEVE, and STT IPsec tunnels are supported. LibreSwan and
StrongSwan IKE daemons are supported. User can choose pre-shared key,
self-signed peer certificate, or CA-signed certificate as authentication
methods.

Signed-off-by: Qiuyu Xiao <qiuyu.xiao.qyx@gmail.com>
Signed-off-by: Ansis Atteka <aatteka@ovn.org>
Co-authored-by: Ansis Atteka <aatteka@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

Makefile.am

@@ -482,6 +482,7 @@ include tests/automake.mk
 include include/automake.mk
 include third-party/automake.mk
 include debian/automake.mk
+include ipsec/automake.mk
 include vswitchd/automake.mk
 include ovsdb/automake.mk
 include rhel/automake.mk

ipsec/automake.mk

@@ -0,0 +1,10 @@
+# Copyright (C) 2017 Nicira, Inc.
+#
+# Copying and distribution of this file, with or without modification,
+# are permitted in any medium without royalty provided the copyright
+# notice and this notice are preserved.  This file is offered as-is,
+# without warranty of any kind.
+
+EXTRA_DIST += \
+        ipsec/ovs-monitor-ipsec
+FLAKE8_PYFILES += ipsec/ovs-monitor-ipsec