Found a few codec inconsistencies between JSON encoders and decoders

- Fix EtherType inconsistency in coding VLAN_PUSH and MPLS_POP instructions
- Fix group id inconsistency in coding a Group instruction
- Fix Group identifiers to be treated as unsigned integers in GroupCodec
- Add a JSON decoder for FlowEntry

Change-Id: Id80b9e009550e3b71b9274adb116e5179391fa66
(cherry picked from commit 494f586853c1a87ba62f20b477e211f996baded5)
diff --git a/core/common/src/test/resources/org/onosproject/codec/impl/simple-flow-entry.json b/core/common/src/test/resources/org/onosproject/codec/impl/simple-flow-entry.json
new file mode 100644
index 0000000..b00ba8d
--- /dev/null
+++ b/core/common/src/test/resources/org/onosproject/codec/impl/simple-flow-entry.json
@@ -0,0 +1,29 @@
+{
+  "priority": 1,
+  "isPermanent": false,
+  "timeout": 1,
+  "deviceId": "of:0000000000000001",
+  "tableId": 1,
+  "treatment": {
+    "instructions": [
+      {
+        "type": "OUTPUT",
+        "port": "CONTROLLER"
+      }
+    ],
+    "deferred": []
+  },
+  "selector": {
+    "criteria": [
+      {
+        "type": "ETH_TYPE",
+        "ethType": "0x800"
+      }
+    ]
+  },
+  "state": "ADDED",
+  "life": 1000,
+  "liveType": "UNKNOWN",
+  "packets": 123,
+  "bytes": 456
+}
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