IPoIB: 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.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>