ospf6d: add "auto-cost reference-bandwidth" command

This command allows the user to change to default reference bandwidth
for cost calculations. The default value is 100 Mbps. With a default
bandwidth of 10 MBps, the default cost becomes 10. Those values are
consistent with OSPFv2.

[DL: resolved conflicts in vty command additions & docs]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/ospf6d/ospf6_snmp.c b/ospf6d/ospf6_snmp.c
index 4660392..4be8be0 100644
--- a/ospf6d/ospf6_snmp.c
+++ b/ospf6d/ospf6_snmp.c
@@ -488,7 +488,9 @@
     case OSPFv3DEMANDEXTENSIONS:
       return SNMP_INTEGER (0);	/* Not supported */
     case OSPFv3REFERENCEBANDWIDTH:
-      return SNMP_INTEGER (100000);
+      if (ospf6)
+        return SNMP_INTEGER (ospf6->ref_bandwidth);
+      /* Otherwise, like for "not implemented". */
     case OSPFv3RESTARTSUPPORT:
     case OSPFv3RESTARTINTERVAL:
     case OSPFv3RESTARTSTRICTLSACHECKING: