igb: rename igb define to be more generic

E1000_MRQC_ENABLE_RSS_4Q enables 4 and 8 queues depending on the part
so rename to be generic.

Similarly, E1000_MRQC_ENABLE_VMDQ_RSS_2Q has no numeric meaning so
rename to be more generic.

Signed-off-by: Todd Fujinaka <todd.fujinaka@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>