DTLS: fix no previous prototype for 'dtls_dissector_add/delete' [-Wmissing-prototypes]

Change-Id: Ib2be8c4ebbaf8492fe76632fae2b5076a44f74ce
Reviewed-on: https://code.wireshark.org/review/11653
Reviewed-by: Michael Mann <mmann78@netscape.net>

epan/dissectors/packet-dtls.c

@@ -58,6 +58,7 @@
 #include <epan/exported_pdu.h>
 #include <wsutil/str_util.h>
 #include "packet-ssl-utils.h"
+#include "packet-dtls.h"
 
 void proto_register_dtls(void);