[EDGEPOD-226] Add installing strongswan to router role

Also fixed ansible-lint failures

Change-Id: I78fbab0a9e2f45ea4f5989c255f09b47ef01bdcc
diff --git a/aether-playbook/roles/router/linux/tasks/interfaces.yml b/aether-playbook/roles/router/linux/tasks/interfaces.yml
new file mode 100644
index 0000000..a9406d8
--- /dev/null
+++ b/aether-playbook/roles/router/linux/tasks/interfaces.yml
@@ -0,0 +1,57 @@
+# Copyright 2020-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+---
+- name: Create netplan config file for SGI and S1U gateway interfaces
+  template:
+    src: etc/netplan/sgi-s1u-gateway.yaml.j2
+    dest: "{{ netplan_config_file }}"
+  notify:
+    - netplan generate
+    - netplan apply
+  tags: router
+
+- name: Install iptables-persistent
+  apt:
+    name: iptables-persistent
+    state: present
+    update_cache: yes
+  tags: router
+
+- name: Ensure ip_forward enabled
+  sysctl:
+    name: net.ipv4.ip_forward
+    value: '1'
+    sysctl_set: yes
+    state: present
+  tags: router
+
+- name: Set default forwarding policy to ACCEPT
+  iptables:
+    chain: FORWARD
+    policy: ACCEPT
+  tags: router
+
+- name: Add SNAT
+  iptables:
+    table: nat
+    chain: POSTROUTING
+    out_interface: "{{ ansible_default_ipv4.interface }}"
+    jump: MASQUERADE
+  tags: router
+
+- name: Save iptables v4 rules
+  shell: iptables-save > /etc/iptables/rules.v4
+  changed_when: False
+  tags: router