net: thunderx: Make hfunc variable const type in nicvf_set_rxfh()

>From struct ethtool_ops:

        int     (*set_rxfh)(struct net_device *, const u32 *indir,
                            const u8 *key, const u8 hfunc);

Change function arg of hfunc to const type.

V2: Fixed indentation.

Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>