igc: Fix NFC rule validation

If we try to overwrite an existing rule with the same filter but
different action, we get EEXIST error as shown below.

$ ethtool -N eth0 flow-type ether dst <MACADDR> action 1 loc 10
$ ethtool -N eth0 flow-type ether dst <MACADDR> action 2 loc 10
rmgr: Cannot insert RX class rule: File exists

The second command is expected to overwrite the previous rule in location
10 and succeed.

This patch fixes igc_ethtool_check_nfc_rule() so it also checks the
rules location. In case they match, the rule under evaluation should not
be considered invalid.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>