Fixed memory leak due to incorrect freeing of DTLS reassembly bit mask

PR#3608

Reviewed-by: Tim Hudson <tjh@openssl.org>
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index 0600f37..c5de193 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -1219,6 +1219,7 @@
 void dtls1_double_timeout(SSL *s);
 int dtls1_send_newsession_ticket(SSL *s);
 unsigned int dtls1_min_mtu(void);
+void dtls1_hm_fragment_free(hm_fragment *frag);
 
 /* some client-only functions */
 int ssl3_client_hello(SSL *s);