add mtu in the sswan profile

roles/vpn/templates/sswan.j2

@@ -1,11 +1,12 @@
 {
     "uuid": "{{ 600000 | random | to_uuid }}",
-    "name": "Algo VPN {{ IP_subject_alt_name }}",
+    "name": "Algo {{ IP_subject_alt_name }}",
     "type": "ikev2-cert",
     "remote": {
         "addr": "{{ IP_subject_alt_name }}"
     },
     "local": {
         "p12": "{{ item.1.stdout }}"
-    }
+    },
+    "mtu": 1280
 }