dns: eve 1 deprecation warning

Redmine issue:
https://redmine.openinfosecfoundation.org/issues/4137

src/output-json-dns.c

@@ -270,6 +270,8 @@ typedef struct LogDnsLogThread_ {
     MemBuffer *buffer;
 } LogDnsLogThread;
 
+static bool v1_deprecation_warned = false;
+
 JsonBuilder *JsonDNSLogQuery(void *txptr, uint64_t tx_id)
 {
     JsonBuilder *queryjb = jb_new_array();
@@ -566,6 +568,12 @@ static DnsVersion JsonDnsParseVersion(ConfNode *conf)
                 version);
     }
 
+    if (!v1_deprecation_warned && version == DNS_VERSION_1) {
+        SCLogWarning(SC_WARN_DEPRECATED, "DNS EVE v1 style logs have been "
+                                         "deprecated and will be removed by May 2022");
+        v1_deprecation_warned = true;
+    }
+
     return version;
 }