octeontx2-pf: Do not modify number of rules

In the ETHTOOL_GRXCLSRLALL ioctl ethtool uses
below structure to read number of rules from the driver.

    struct ethtool_rxnfc {
            __u32                           cmd;
            __u32                           flow_type;
            __u64                           data;
            struct ethtool_rx_flow_spec     fs;
            union {
                    __u32                   rule_cnt;
                    __u32                   rss_context;
            };
            __u32                           rule_locs[0];
    };

Driver must not modify rule_cnt member. But currently driver
modifies it by modifying rss_context. Hence fix it by using a
local variable.

Fixes: 81a43620

 ("octeontx2-pf: Add RSS multi group support")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>