fabric: add some Cumulus defaults to mgmt interface config

roles/fabric/templates/interfaces.j2

@@ -4,6 +4,7 @@ source /etc/network/interfaces.d/*.intf
 auto mgmt
 iface mgmt
     address 127.0.0.1/8
+    address 127.0.1.1/8
     address ::1/128
     vrf-table auto
 
@@ -11,6 +12,8 @@ iface mgmt
 auto {{ iface.name }}
 iface {{ iface.name }}
     vrf mgmt
+    ip-forward off
+    ip6-forward off
 {% for ip in iface.ip_addresses | rejectattr('address', 'match', '^fe80::.*/64$' ) %}
     address {{ ip.address }}
 {% endfor %}