add the option to specify the family per rule to support ipv6 (#3)

Closes: #2 

* add the option to specify the family per rule to support ipv6

* include policy updates for ipv6

* update documentation to mention ipv6

* Make ipv6 optional; remove spurious tabs from the readme.

* set ipv6 policies only if ipv6 is enabled on the host and not explicitly turned off for this service

README.rst

     parametetrs:
       iptables:
         service:
+          enabled: True
           chain:
             INPUT:
               rules:
                   source_network: 192.168.1.0/24
                   jump: ACCEPT
 
+IPv6 is supported as well
+
+.. code-block:: yaml
+
+    parameters:
+      iptables:
+        service:
+          enabled: True
+          ipv6: True
+          chain:
+            INPUT:
+              rules:
+                - protocol: tcp
+                  family: ipv6
+                  destination_port: 22
+                  source_network: 2001:DB8::/32
+                  jump: ACCEPT
+
 Read more
 =========
 

iptables/_rule.sls

   {%- endif %}
   - table: {{ rule.get('table', 'filter') }}
   - chain: {{ chain_name }}
+  {%- if rule.family is defined %}
+  - family: {{ rule.family }}
+  {%- endif %}
   {%- if rule.jump is defined %}
   - jump: {{ rule.jump }}
   {%- endif %}

iptables/rules.sls

 {%- if chain.policy is defined %}
 iptables_{{ chain_name }}_policy:
   iptables.set_policy:
+    - family: ipv4
     - chain: {{ chain_name }}
     - policy: {{ chain.policy }}
     - table: filter
+
+{%-   if grains.ipv6|default(False) and service.ipv6|default(True) %}
+iptables_{{ chain_name }}_ipv6_policy:
+  iptables.set_policy:
+    - family: ipv6
+    - chain: {{ chain_name }}
+    - policy: {{ chain.policy }}
+    - table: filter
+{%-   endif %}
 {%- endif %}
 
 {%- for service_name, service in pillar.items() %}

iptables/service.sls

     - table: filter
     - require_in:
       - iptables: iptables_flush
+
+{%-   if grains.ipv6|default(False) and service.ipv6|default(True) %}
+iptables_{{ chain_name }}_ipv6_policy:
+  iptables.set_policy:
+    - chain: {{ chain_name }}
+    - family: ipv6
+    - policy: ACCEPT
+    - table: filter
+    - require_in:
+      - iptables: ip6tables_flush
+{%-   endif %}
+
 {%- endfor %}
 
 iptables_flush:
   iptables.flush
 
+{%- if grains.ipv6|default(False) and service.ipv6|default(True) %}
+ip6tables_flush:
+  iptables.flush:
+    - family: ipv6
+{%- endif %}
+
+
 {%- endif %}