Recover dual-homed host failover using pair link

In addition,
- Block ARP/NDP on pair port from being sent to controller
- Block DAD on pair port from flooded back to the originated host
- Minor refactoring

Change-Id: I3d697a06cb7ed3b56baa5d490197c155fe6969f0
diff --git a/src/main/java/org/onosproject/segmentrouting/config/SegmentRoutingDeviceConfig.java b/src/main/java/org/onosproject/segmentrouting/config/SegmentRoutingDeviceConfig.java
index 706c549..7959df6 100644
--- a/src/main/java/org/onosproject/segmentrouting/config/SegmentRoutingDeviceConfig.java
+++ b/src/main/java/org/onosproject/segmentrouting/config/SegmentRoutingDeviceConfig.java
@@ -82,7 +82,7 @@
                 isEdgeRouter() != null &&
                 adjacencySids() != null &&
                 // pairDeviceId and pairLocalPort must be both configured or both omitted
-                !(hasField(PAIR_DEVICE_ID) ^ hasField(PAIR_LOCAL_PORT)) &&
+                (hasField(PAIR_DEVICE_ID) == hasField(PAIR_LOCAL_PORT)) &&
                 (!hasField(PAIR_DEVICE_ID) || pairDeviceId() != null) &&
                 (!hasField(PAIR_LOCAL_PORT) || pairLocalPort() != null);
     }