tcp_accepted(): check pcb state to verify it isn't called on a connection-pcb

src/include/lwip/tcp.h

@@ -328,9 +328,12 @@ void             tcp_err     (struct tcp_pcb *pcb, tcp_err_fn err);
 #define          tcp_nagle_disabled(pcb)  (((pcb)->flags & TF_NODELAY) != 0)
 
 #if TCP_LISTEN_BACKLOG
-#define          tcp_accepted(pcb) (((struct tcp_pcb_listen *)(pcb))->accepts_pending--)
+#define          tcp_accepted(pcb) do { \
+  LWIP_ASSERT("pcb->state == LISTEN (called for wrong pcb?)", pcb->state == LISTEN); \
+  (((struct tcp_pcb_listen *)(pcb))->accepts_pending--); } while(0)
 #else  /* TCP_LISTEN_BACKLOG */
-#define          tcp_accepted(pcb) LWIP_UNUSED_ARG(pcb);
+#define          tcp_accepted(pcb) LWIP_ASSERT("pcb->state == LISTEN (called for wrong pcb?)", \
+                                               pcb->state == LISTEN)
 #endif /* TCP_LISTEN_BACKLOG */
 
 void             tcp_recved  (struct tcp_pcb *pcb, u16_t len);