build: treat opaque-lsa default correctly for ospfapi

In deciding whether to default ospfapi to on or off, use the same rule
for opaque-lsa as earlier: != no rather than = yes, so that not having
set it implies yes.
diff --git a/configure.ac b/configure.ac
index 27d26ef..b981d5b 100755
--- a/configure.ac
+++ b/configure.ac
@@ -1200,7 +1200,7 @@
 fi
 
 OSPFCLIENT=""
-if test "${enable_opaque_lsa}" = "yes"; then
+if test "${enable_opaque_lsa}" != "no"; then
   if test "${enable_ospfapi}" != "no";then
     AC_DEFINE(SUPPORT_OSPF_API,,OSPFAPI)