[ONOS-7808] Support P4Runtime default table entries

We achieve this by creating a special mirror to store the original
default entries as specified in the P4 program. Applications can modify
the default entry by inserting flow rules with empty selectors. When
removing such flow rule, the default table entry is restored to the
original one as stored in the mirror.

Change-Id: Ib11a7172ab56be7cbbd23022e4b62ed6b70b6eca
diff --git a/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-spgw-int/bmv2/default/bmv2.json b/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-spgw-int/bmv2/default/bmv2.json
index 1e044cc..f98e55d 100644
--- a/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-spgw-int/bmv2/default/bmv2.json
+++ b/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-spgw-int/bmv2/default/bmv2.json
@@ -12260,9 +12260,9 @@
           },
           "default_entry" : {
             "action_id" : 5,
-            "action_const" : true,
+            "action_const" : false,
             "action_data" : [],
-            "action_entry_const" : true
+            "action_entry_const" : false
           }
         },
         {