ucc_geth: Move freeing of TX packets to NAPI context

This will make the system alot more responsive while ping flooding the
ucc_geth ethernet interface.

Also set NAPI weight to 64 as this is a common value.

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>