ntp: avoid truncation of NTPv4 MACs by default

If the MAC in NTPv4 requests would be truncated, use version 3 by
default to avoid the truncation. This is necessary for compatibility
with older chronyd servers, which do not respond to messages with
truncated MACs.

keys.c

@@ -322,6 +322,22 @@ KEY_GetAuthDelay(uint32_t key_id)
 
 /* ================================================== */
 
+int
+KEY_GetAuthLength(uint32_t key_id)
+{
+  unsigned char buf[MAX_HASH_LENGTH];
+  Key *key;
+
+  key = get_key_by_id(key_id);
+
+  if (!key)
+    return 0;
+
+  return HSH_Hash(key->hash_id, buf, 0, buf, 0, buf, sizeof (buf));
+}
+
+/* ================================================== */
+
 int
 KEY_CheckKeyLength(uint32_t key_id)
 {