i40e: init flow control settings to disabled

Refactor flow control set up and disable L2 flow
control by default.

Change-Id: I2fe257b80df6d9a1e37deb4df118da8f8467040d
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>