MINOR: dns: dns_nameserver structure update: new counter for truncated response

This patch updates the dns_nameserver structure to integrate a counter
dedicated to 'truncated' response sent by servers.
Such response are important to track, since HAProxy is supposed to
replay its request.
diff --git a/src/dumpstats.c b/src/dumpstats.c
index 01fe53b..92f2dea 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -6266,6 +6266,7 @@
 			chunk_appendf(&trash, "  other: %ld\n", pnameserver->counters.other);
 			chunk_appendf(&trash, "  invalid: %ld\n", pnameserver->counters.invalid);
 			chunk_appendf(&trash, "  too_big: %ld\n", pnameserver->counters.too_big);
+			chunk_appendf(&trash, "  truncated: %ld\n", pnameserver->counters.truncated);
 			chunk_appendf(&trash, "  outdated: %ld\n", pnameserver->counters.outdated);
 		}