[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
(cherry picked from commit e9ba39c13a5c79dc71b2c4d34c225a5c3c2e129e)
diff --git a/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-full/bmv2/default/bmv2.json b/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-full/bmv2/default/bmv2.json
index 83da36b..e300f55 100644
--- a/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-full/bmv2/default/bmv2.json
+++ b/pipelines/fabric/impl/src/main/resources/p4c-out/fabric-full/bmv2/default/bmv2.json
@@ -15945,9 +15945,9 @@
           },
           "default_entry" : {
             "action_id" : 8,
-            "action_const" : true,
+            "action_const" : false,
             "action_data" : [],
-            "action_entry_const" : true
+            "action_entry_const" : false
           }
         },
         {