ixgbe: Refactor MAC address configuration code

In the process of tracking down a memory leak when adding/removing FDB
entries I had to go through the MAC address configuration code for ixgbe.
In the process of doing so I found a number of issues that impacted
readability and performance.  This change updates the code in general to
clean it up so it becomes clear what each step is doing.  From what I can
tell there a couple of bugs cleaned up in this code.

First is the fact that the MAC addresses were being double counted for the
PF.  As a result once entries up to 63 had been used you could no longer
add additional filters.

A simple test case for this:
  for i in `seq 0 96`
  do
    ip link add link ens8 name mv$i type macvlan
    ip link set dev mv$i up
  done

Test script:
  ethregs -s 0:8.0 | grep -e "RAH" | grep 8000....$

When things are working correctly RAL/H registers 1 - 97 will be consumed.
In the failing case it will stop at 63 and prevent any further filters from
being added.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>