drivers: wifi: esp: flush socket work items in socket put

There might be some scheduled work related to socket currently requested
to be destroyed/closed. Schedule a dummy work to make sure all
previously running work items in workqueue are finished.

When talking about TX packets, this makes sure that all previously
scheduled data is actually sent (flushed) before closing socket.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>