net/mlx4_en: fix mlx4 ethtool -N insertion

ethtool expects ETHTOOL_GRXCLSRLALL to set ethtool_rxnfc->data with the
total number of entries in the rx classifier table.  Surprisingly, mlx4
is missing this part (in principle ethtool could still move forward and
try the insert).

Tested: compiled and run command:
	phh13:~# ethtool -N eth1 flow-type udp4  queue 4
	Added rule with ID 255

Signed-off-by: Luigi Rizzo <lrizzo@google.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>