Define default DNS lookup order.

src/belle_sip_resolver.c

@@ -72,6 +72,14 @@ static struct dns_resolv_conf *resconf(belle_sip_resolver_context_t *ctx) {
 	}
 #endif
 
+	/* If the lookup order has not been initialized, initialize it now to the following order:
+	   1. file
+	   2. cache
+	   3. bind
+	*/
+	if (ctx->resconf->lookup[0] == '\0') {
+		strncpy(ctx->resconf->lookup, "fcb", sizeof ctx->resconf->lookup);
+	}
 
 	return ctx->resconf;
 }

src/dns.c

@@ -4388,7 +4388,6 @@ int dns_resconf_loadfromresolv(struct dns_resolv_conf *resconf) {
     	memcpy(&resconf->nameserver[i],&addresses[i],sizeof(union res_sockaddr_union));
     }
     res_ndestroy(&res);
-    strncpy(resconf->lookup, "fcb", sizeof resconf->lookup);
     return i>0?0:-1;
 }
 #endif /*HAVE_RESINIT*/