ixgbe: add flow control ethertype to the anti-spoofing filter

This patch makes sure that flow control packets initiated by the VF are
dropped and reported as spoofed.

Flow control packets can be used to limit the throughput or as DOS
attack when generated from a VF. Flow control is not supported per VF
hence any pause frames generated from a VF are considered malicious.

Also cleaned up indentation and some redundant comments.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>