Adding struct member is ABI breaker however as the structure is always allocated by
the library calls we just move it to the end and it should be reasonably safe.
diff -up openssl-1.0.0-beta4/ssl/dtls1.h.dtls1-abi openssl-1.0.0-beta4/ssl/dtls1.h
--- openssl-1.0.0-beta4/ssl/dtls1.h.dtls1-abi	2009-11-12 14:34:37.000000000 +0100
+++ openssl-1.0.0-beta4/ssl/dtls1.h	2009-11-12 14:47:57.000000000 +0100
@@ -216,9 +216,6 @@ typedef struct dtls1_state_st
 	 */
 	record_pqueue buffered_app_data;
 
-	/* Is set when listening for new connections with dtls1_listen() */
-	unsigned int listen;
-
 	unsigned int mtu; /* max DTLS packet size */
 
 	struct hm_header_st w_msg_hdr;
@@ -242,6 +239,9 @@ typedef struct dtls1_state_st
 	unsigned int retransmitting;
 	unsigned int change_cipher_spec_ok;
 
+	/* Is set when listening for new connections with dtls1_listen() */
+	unsigned int listen;
+
 	} DTLS1_STATE;
 
 typedef struct dtls1_record_data_st