Don't keep creating CONNECTION_CLOSE frames

If we want to send a CONNECTION_CLOSE frame then one is enough unless we
are scheduled to send another one. Now that we can create more than one
datagram in one go this is now required.

include/internal/quic_txpim.h

@@ -40,6 +40,7 @@ typedef struct quic_txpim_pkt_st {
     unsigned int        had_max_streams_bidi_frame  : 1;
     unsigned int        had_max_streams_uni_frame   : 1;
     unsigned int        had_ack_frame               : 1;
+    unsigned int        had_conn_close              : 1;
 
     /* Private data follows. */
 } QUIC_TXPIM_PKT;

ssl/quic/quic_txp.c

@@ -1806,6 +1806,7 @@ static int txp_generate_pre_token(OSSL_QUIC_TX_PACKETISER *txp,
             if (!tx_helper_commit(h))
                 return 0;
 
+            tpkt->had_conn_close = 1;
             *can_be_non_inflight = 0;
         } else {
             tx_helper_rollback(h);
@@ -2946,6 +2947,9 @@ static int txp_pkt_commit(OSSL_QUIC_TX_PACKETISER *txp,
     if (tpkt->had_ack_frame)
         txp->want_ack &= ~(1UL << pn_space);
 
+    if (tpkt->had_conn_close)
+        txp->want_conn_close = 0;
+
     /*
      * Decrement probe request counts if we have sent a packet that meets
      * the requirement of a probe, namely being ACK-eliciting.

ssl/quic/quic_txpim.c

@@ -115,6 +115,7 @@ static void txpim_clear(QUIC_TXPIM_PKT_EX *ex)
     ex->public.had_max_streams_bidi_frame  = 0;
     ex->public.had_max_streams_uni_frame   = 0;
     ex->public.had_ack_frame               = 0;
+    ex->public.had_conn_close              = 0;
 }
 
 QUIC_TXPIM_PKT *ossl_quic_txpim_pkt_alloc(QUIC_TXPIM *txpim)