Revert "net: tcp: Fix ref counting for the net_pkt"

This reverts commit 9cd547f.

The commit we are reverting, fixed originally the issue that was
seen with zperf. There we freed the net_pkt too early while it was
still waiting for a TCP ACK. The commit 9cd547f seemd to fix that
issue but it was causing issues in dump_http_server sample app which
then started to leak memory. No issues were seen with echo-server
with or without the commit 9cd547f.

So the lessons learned here is that one needs to test with multiple
network sample apps like dump_http_server, echo_server and zperf
before considering TCP fixes valid, especially fixes that touch
ref counting issues.

Fixes #15031

The next commit will fix the zperf free memory access patch.

Signed-off-by: Jukka Rissanen <[email protected]>

subsys/net/ip/tcp.c

@@ -229,17 +229,10 @@ static void tcp_retry_expired(struct k_work *work)
 		pkt = CONTAINER_OF(sys_slist_peek_head(&tcp->sent_list),
 				   struct net_pkt, sent_list);
 
-		/* In the retry case, the original ref (when the packet
-		 * was created) is set to 1. That original ref was
-		 * decremented when the packet was sent by the driver.
-		 * We need to restore that original ref so that the
-		 * device driver will not remove the retry packet that
-		 * we just sent. Earlier we also checked net_pkt_sent(pkt)
-		 * here but that is not correct as then the packet that was
-		 * sent first time, was removed by the driver and we got
-		 * access to memory already freed.
-		 */
-		do_ref_if_needed(tcp, pkt);
+		if (net_pkt_sent(pkt)) {
+			do_ref_if_needed(tcp, pkt);
+			net_pkt_set_sent(pkt, false);
+		}
 
 		net_pkt_set_queued(pkt, true);