sync zebra routing table with the kernel one when interface is down

Add router to kernel main router table with "ip", then you can see 
a router item in kernel main router table. Also can see this router
item in zebra router table. If down the interface, this router item
will be deleted from kernel main router table, but it will not be 
deleted from zebra router table, just set as inactive.

This patch is adopted from [1].
[1] http://www.gossamer-threads.com/lists/quagga/dev/22609

Upstream-Status: Pending

Signed-of-by: Aws Ismail <aws.ismail@windriver.com>
Signed-of-by: Roy.Li <rongqing.li@windriver.com>

---
 zebra/zebra_rib.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
index 154e8d5..63434d0 100644
--- a/zebra/zebra_rib.c
+++ b/zebra/zebra_rib.c
@@ -765,6 +765,9 @@ rib_match_ipv6 (struct in6_addr *addr)
 #define RIB_SYSTEM_ROUTE(R) \
         ((R)->type == ZEBRA_ROUTE_KERNEL || (R)->type == ZEBRA_ROUTE_CONNECT)
 
+#define RIB_KERNEL_ROUTE(R) \
+	((R)->type == ZEBRA_ROUTE_KERNEL)
+
 /* This function verifies reachability of one given nexthop, which can be
  * numbered or unnumbered, IPv4 or IPv6. The result is unconditionally stored
  * in nexthop->flags field. If the 4th parameter, 'set', is non-zero,
@@ -1135,6 +1138,10 @@ rib_process (struct route_node *rn)
       redistribute_delete (&rn->p, fib);
       if (! RIB_SYSTEM_ROUTE (fib))
 	rib_uninstall_kernel (rn, fib);
+#ifdef GNU_LINUX
+      else if(RIB_KERNEL_ROUTE (fib) && !if_is_up(if_lookup_by_index(fib->nexthop->ifindex)))
+	del=fib;
+#endif
       UNSET_FLAG (fib->flags, ZEBRA_FLAG_SELECTED);
 
       /* Set real nexthop. */
-- 
1.7.4.1