Cellular: Add PPP/IP config flags in CellularInterface.json

Author: Ari Parkkila

tools/test_configs/CellularInterface.json

@@ -37,7 +37,9 @@
             "ppp-cell-iface.apn-lookup": false,
             "cellular.use-apn-lookup": false,
             "lwip.ipv4-enabled": true,
+            "ppp.ipv4-enabled": true,
             "lwip.ipv6-enabled": true,
+            "ppp.ipv6-enabled": true,
             "lwip.tcp-enabled": true,
             "lwip.ppp-enabled": true,
             "lwip.ethernet-enabled": false,