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

This reverts commit 9cd547f5.

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 9cd547f5 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 9cd547f5.

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 <jukka.rissanen@linux.intel.com>