Added json configuration file and mbed ignore file to lwip stack.

features/net/FEATURE_IPV4/lwip-interface/.mbedignore

@@ -0,0 +1,7 @@
+lwip/doc/*
+lwip/test/*
+lwip/src/apps/*
+lwip/src/netif/ppp/*
+lwip/src/netif/lwip_slipif.c
+lwip/src/include/lwip/apps/*
+lwip/src/include/posix/*

features/net/FEATURE_IPV4/lwip-interface/mbed_lib.json

@@ -0,0 +1,21 @@
+{
+    "name": "lwip",
+    "config": {
+        "ipv4-enabled": {
+            "help": "Enable IPv4",
+            "value": true
+        },
+        "ipv6-enabled": {
+            "help": "Enable IPv6",
+            "value": false
+        },
+        "ip-ver-pref": {
+            "help": "On dual stack system the preferred stack: 4 for IPv4 and 6 for IPv6",
+            "value": 4
+        },
+        "addr-timeout": {
+            "help": "On dual stack system how long to wait preferred stack's address in seconds",
+            "value": 5
+        }
+    }
+}