net.c: fix PDU find bug in coap_remove_from_queue()

Issue #163 [1] points out that coap_remove_from_queue() may release
the wrong PDU from the retransmit queue due to a false hit in the
do/while loop. This change was proposed by hongnguyen-tma to fix
this issue.

[1] #163

src/net.c

@@ -1310,7 +1310,7 @@ coap_remove_from_queue(coap_queue_t **queue, coap_session_t *session, coap_tid_t
   do {
     p = q;
     q = q->next;
-  } while (q && session != q->session && id != q->id);
+  } while (q && (session != q->session || id != q->id));
 
   if (q) {			/* found transaction */
     p->next = q->next;