ixgbe: Cleanup FDB handling code

This change makes it so that the behavior for FDB handling is consistent
between both the SR-IOV and non-SR-IOV cases.  The main change here is that we
perform bounds checking on the number of SR-IOV addresses regardless of if
SR-IOV is enabled or not as we can only support a certain number of addresses
in the hardware.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>