net: lwip: rename linkoutput() as net_lwip_tx()

Rename static function linkoutput() as net_lwip_tx() for consistency
with net_lwip_rx().

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
1 file changed