igc: Align terms used in NFC support code

The Network Flow Classification (NFC) support code from IGC driver uses
terms such as 'rule', 'filter', 'entry', 'input' interchangeably when
referring to NFC rules, making it harder to follow the code. This patch
renames IGC's internal APIs, structs, and variables so we stick with the
term 'rule' since this is the term used in ethtool APIs. It also removes
some not applicable comments along the way. No functionality is changed
by this patch.

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>