zebra: Fix change of distance on ipv6 route creating duplicate routes

If you enter:

ipv6 route 2002:44:44:44::44/128 swp1 4
ipv6 route 2002:44:44:44::44/128 swp1 99

You get:

host-111# show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
O - OSPFv6, I - IS-IS, B - BGP, A - Babel, T - Table,
> - selected route, * - FIB route
S 2002:44:44:44::44/128 [99/0] is directly connected, swp1
S>* 2002:44:44:44::44/128 [4/0] is directly connected, swp1

This problem is fixed in the ipv4 code path.  Copying the same
code from the ipv4 into the ipv6 code path fixes the issue.

With the fix:

host-111(config)# ipv6 route 2002:44:44:44::44/128 swp1 4
host-111(config)# do show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
       O - OSPFv6, I - IS-IS, B - BGP, A - Babel, T - Table,
       > - selected route, * - FIB route

S>* 2002:44:44:44::44/128 [4/0] is directly connected, swp1
C * fe80::/64 is directly connected, swp1
C>* fe80::/64 is directly connected, eth0
host-111(config)# ipv6 route 2002:44:44:44::44/128 swp1 99
host-111(config)# do show ipv6 route
Codes: K - kernel route, C - connected, S - static, R - RIPng,
       O - OSPFv6, I - IS-IS, B - BGP, A - Babel, T - Table,
       > - selected route, * - FIB route

S>* 2002:44:44:44::44/128 [99/0] is directly connected, swp1
C * fe80::/64 is directly connected, swp1
C>* fe80::/64 is directly connected, eth0
host-111(config)#

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
index 6a54f11..0efa88d 100644
--- a/zebra/zebra_rib.c
+++ b/zebra/zebra_rib.c
@@ -2866,6 +2866,7 @@
   struct static_route *si;
   struct static_route *pp;
   struct static_route *cp;
+  struct static_route *update = NULL;
   struct zebra_vrf *zvrf = vrf_info_get (vrf_id);
   struct route_table *stable = zvrf->stable[AFI_IP6][SAFI_UNICAST];
 
@@ -2886,16 +2887,23 @@
   /* Do nothing if there is a same static route.  */
   for (si = rn->info; si; si = si->next)
     {
-      if (distance == si->distance 
-	  && type == si->type
+      if (type == si->type
 	  && (! gate || IPV6_ADDR_SAME (gate, &si->addr.ipv6))
 	  && (! ifname || strcmp (ifname, si->ifname) == 0))
 	{
-	  route_unlock_node (rn);
-	  return 0;
+	  if (distance == si->distance)
+	    {
+	      route_unlock_node (rn);
+	      return 0;
+	    }
+	  else
+	    update = si;
 	}
     }
 
+  if (update)
+    static_delete_ipv6(p, type, gate, ifname, si->distance, vrf_id);
+
   /* Make new static route structure. */
   si = XCALLOC (MTYPE_STATIC_ROUTE, sizeof (struct static_route));