forcedeth: Kill NAPI config options.

All distributions enable it, therefore no significant body of users
are even testing the driver with it disabled.  And making NAPI
configurable is heavily discouraged anyways.

I left the MSI-X interrupt enabling thing in an "#if 0" block
so hopefully someone can debug that and it can get re-enabled.
Probably it was just one of the NVIDIA chipset MSI erratas that
we work handle these days in the PCI quirks (see drivers/pci/quirks.c
and stuff like nvenet_msi_disable()).

Signed-off-by: David S. Miller <davem@davemloft.net>