netxen: lower NAPI weight

Since commit 82dc3c63 ("net: introduce NAPI_POLL_WEIGHT")
netif_napi_add() produces an error message if a NAPI poll weight
greater than 64 is requested.

Use the standard NAPI weight.

v2: proper reference to the related commit

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>