net: tc: Return information whether TX pkt was queued

We need to know whether the net_pkt was successfully placed
to transmit queue. It is possible in TX side, that the net_pkt
is already in TX queue when for example TCP packet is
re-transmitted, in which case the queue submit will fail.
This cannot happen in RX side as there are no timers involved.

It is required to check about such pending flag before trying to submit
it into the queue. Indeed, the work queue could be scheduled right after
such queuing, thus checking for the pending flag afterwards would
provide a false information.

It is unfortunate k_work_submit_to_queue() does not return anything as
it would simplify the code then.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>