i40e: Fix the case where per TC queue count was higher than queues enabled

When the driver or hardware gets less interrupt vectors than the actual
number of CPU cores, limit the queue count for the priority queue
traffic class (TC) queues.

This will fix a warning with multiple function mode where systems
regularly have more cores than vectors.

Also add extra comment for readability.

Change-ID: I4f02226263aa3995e1f5ee5503eac0cd6ee12fbd
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>