pimd: send pim prune via correct interface when rpf upstream interface for a source changes

When the rpf upstream interface for a joined source changes, a prune was
being sent out the new rpf upstream interface that was intended for the old
upstream router.  The prune should be sent out the old rpf upstream
interface so that the old route for the multicast source is pruned.

Reviewed-by: Jafar Al-Gharaibeh <jafar@atcorp.com>
Signed-off-by: Taylor Bouvin <tbouvin@atcorp.com>
Tested-by: NetDEF CI System <cisystem@netdef.org>
diff --git a/pimd/pim_rpf.h b/pimd/pim_rpf.h
index 078e89f..9a48ea0 100644
--- a/pimd/pim_rpf.h
+++ b/pimd/pim_rpf.h
@@ -31,6 +31,6 @@
 int pim_nexthop_lookup(struct pim_nexthop *nexthop,
 		       struct in_addr addr);
 enum pim_rpf_result pim_rpf_update(struct pim_upstream *up,
-				   struct in_addr *old_rpf_addr);
+				   struct pim_rpf *old_rpf);
 
 #endif /* PIM_RPF_H */