pimd: Add ability to set DR Priority for an interface

From RFC 4601, Section 4.3.1:

The DR_Priority Option allows a network administrator to give
preference to a particular router in the DR election process by
giving it a numerically larger DR Priority.  The DR_Priority Option
SHOULD be included in every Hello message, even if no DR Priority is
explicitly configured on that interface.  This is necessary because
priority-based DR election is only enabled when all neighbors on an
interface advertise that they are capable of using the DR_Priority
Option.  The default priority is 1.

This modification allows the setting of the DR Priority on a per
interface basis.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/pimd/pim_neighbor.h b/pimd/pim_neighbor.h
index 8f19c75..5b2172d 100644
--- a/pimd/pim_neighbor.h
+++ b/pimd/pim_neighbor.h
@@ -69,6 +69,6 @@
 			 struct list *addr_list);
 struct prefix *pim_neighbor_find_secondary(struct pim_neighbor *neigh,
 					   struct in_addr addr);
-void pim_if_dr_election(struct interface *ifp);
+int pim_if_dr_election(struct interface *ifp);
 
 #endif /* PIM_NEIGHBOR_H */