atl1c: use netif_napi_add_tx() for Tx NAPI

Use netif_napi_add_tx() for NAPI in Tx direction instead of the regular
netif_napi_add() function.

Signed-off-by: Sieng-Piaw Liew <liew.s.piaw@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>