MINOR: dns: New DNS response analysis code: DNS_RESP_TRUNCATED

This patch introduces a new internal response state about the analysis
of a DNS response received by a server.
It is dedicated to report to above layer that the response is
'truncated'.
diff --git a/src/server.c b/src/server.c
index 9bbed79..ca8c4f8 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2132,6 +2132,7 @@
 			break;
 
 		case DNS_RESP_ANCOUNT_ZERO:
+		case DNS_RESP_TRUNCATED:
 		case DNS_RESP_ERROR:
 			if (resolution->query_type == DNS_RTYPE_ANY) {
 				/* let's change the query type */