bnxt_en: Check hardware resources before enabling NTUPLE.

The hardware resources required to enable NTUPLE varies depending on
how many rx channels are configured.  We need to make sure we have the
resources before we enable NTUPLE.  Add bnxt_rfs_capable() to do the
checking.

In addition, we need to do the same checking in ndo_fix_features().  As
the rx channels are changed using ethtool -L, we call
netdev_update_features() to make the necessary adjustment for NTUPLE.

Calling netdev_update_features() in netif_running() state but before
calling bnxt_open_nic() would be a problem.  To make this work,
bnxt_set_features() has to be modified to test for BNXT_STATE_OPEN for
the true hardware state instead of checking netif_running().

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>