Avoid infinite loop where we reschedule for the current second by

adding one. We might expire a lease a second late, but that's okay.

See RT ticket #17112 for more.

RELNOTES

@@ -65,6 +65,9 @@ suggested fixes to <dhcp-users@isc.org>.
   but would not return the address in response to a REQUEST. Thanks to
   Dennis Kou for finding the bug.
 
+- Fixed an error causing the server to lock up on lease expiration,
+  reported independently by Jothilingam Vasu and Dennis Kou.
+
 			Changes since 4.0.0a2
 
 - Fix for startup where there are no IPv4 addresses on an interface.

server/mdb6.c

@@ -1046,7 +1046,7 @@ schedule_lease_timeout(struct ipv6_pool *pool) {
 		tmp = (struct iaaddr *)isc_heap_element(pool->active_timeouts, 
 							1);
 		if (tmp->valid_lifetime_end_time < next_timeout) {
-			next_timeout = tmp->valid_lifetime_end_time;
+			next_timeout = tmp->valid_lifetime_end_time + 1;
 		}
 	}