Fix broken encoding of keep alive messages

The encoding was broken by the recent changes that added
encryption support for HI1 notifications.

Author: salcock

src/collector/etsiencoding/tripayload.c

@@ -99,6 +99,7 @@ wandder_encoded_result_t *encode_etsi_keepalive(wandder_encoder_t *encoder,
     struct timeval tv;
 
     gettimeofday(&tv, NULL);
+    ENC_USEQUENCE(encoder);
     encode_etsili_pshdr(encoder, hdrdata, 0, seqno, &tv, timefmt);
     ENC_CSEQUENCE(encoder, 2);          // Payload
     ENC_CSEQUENCE(encoder, 2);          // TRIPayload