ospf6d: implement admin distance

Until today the admin distance cannot be configured for any IPv6
routing protocol. This patch implements it for ospf6.

Signed-off-by: Maitane Zotes <maz@open.ch>
diff --git a/lib/memtypes.c b/lib/memtypes.c
index 6df1448..3b9345d 100644
--- a/lib/memtypes.c
+++ b/lib/memtypes.c
@@ -234,6 +234,7 @@
   { MTYPE_OSPF6_NEXTHOP,      "OSPF6 nexthop"			},
   { MTYPE_OSPF6_EXTERNAL_INFO,"OSPF6 ext. info"			},
   { MTYPE_OSPF6_OTHER,        "OSPF6 other"			},
+  { MTYPE_OSPF6_DISTANCE,     "OSPF6 distance"			},
   { -1, NULL },
 };