ospf6d: fix uninitialized warning in SNMP

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/ospf6d/ospf6_snmp.c b/ospf6d/ospf6_snmp.c
index ef44e4c..307d420 100644
--- a/ospf6d/ospf6_snmp.c
+++ b/ospf6d/ospf6_snmp.c
@@ -628,7 +628,7 @@
   int len;
   oid *offset;
   int offsetlen;
-  struct ospf6_area *oa;
+  struct ospf6_area *oa = NULL;
   struct listnode *node;
   struct interface *iif;
   struct ospf6_interface *oi = NULL;