Added IPv6 routing support to SDN-IP, and integrated it with BGP:
 * The routing entries as received from BGP can be either IPv4 or IPv6
 * The CLI prints the IPv4 and IPv6 routes
 * The BGP peering is still over IPv4, so configuration-wise the IPv6
   routes from the eBGP peers have to be configured to use the IPv4 peering.
 * The integration/testing with the IPv6 Network Discovery Protocol is not
   done yet.
 * The integration/testing with IPv6 intents is not done yet.

Also:
 * Moved nested class BgpSessionManager.BgpRouteSelector out of the
   BgpSessionManager class.
 * Code cleanup.

Change-Id: I9f2dbe4395a72d353bbf215a8a14b01b53c3423f
diff --git a/apps/sdnip/src/main/java/org/onosproject/sdnip/SdnIpService.java b/apps/sdnip/src/main/java/org/onosproject/sdnip/SdnIpService.java
index cfa089a..aa71f02 100644
--- a/apps/sdnip/src/main/java/org/onosproject/sdnip/SdnIpService.java
+++ b/apps/sdnip/src/main/java/org/onosproject/sdnip/SdnIpService.java
@@ -32,18 +32,32 @@
     public Collection<BgpSession> getBgpSessions();
 
     /**
-     * Gets the BGP routes.
+     * Gets the selected IPv4 BGP routes among all BGP sessions.
      *
-     * @return the BGP routes
+     * @return the selected IPv4 BGP routes among all BGP sessions
      */
-    public Collection<BgpRouteEntry> getBgpRoutes();
+    public Collection<BgpRouteEntry> getBgpRoutes4();
 
     /**
-     * Gets all the routes known to SDN-IP.
+     * Gets the selected IPv6 BGP routes among all BGP sessions.
      *
-     * @return the SDN-IP routes
+     * @return the selected IPv6 BGP routes among all BGP sessions
      */
-    public Collection<RouteEntry> getRoutes();
+    public Collection<BgpRouteEntry> getBgpRoutes6();
+
+    /**
+     * Gets all IPv4 routes known to SDN-IP.
+     *
+     * @return the SDN-IP IPv4 routes
+     */
+    public Collection<RouteEntry> getRoutes4();
+
+    /**
+     * Gets all IPv6 routes known to SDN-IP.
+     *
+     * @return the SDN-IP IPv6 routes
+     */
+    public Collection<RouteEntry> getRoutes6();
 
     /**
      * Changes whether this SDN-IP instance is the primary or not based on the