ixl: Update to 1.4.20-k.

Changes by author:

Eric Joyner ixl: Add more error messages/checks to ixl_vsi_assign_msix().
Eric Joyner ixl/ixlv: Clarify a comment about descriptors.
Eric Joyner ixl/ixlv: Improve i40e_debug() implementation.
Eric Joyner ixl/ixlv: Remove unused ASSERT() macro; move struct around.
Eric Joyner ixl: Set initial advertised speed value in init_locked().
Eric Joyner ixl: Fix flow control sysctl value being stored when new value is invalid.
Eric Joyner Edit comments and spacing.
Carolyn Wyborny i40e-shared: Add functions to blink led on Coppervale PHY
Eric Joyner ixl: Re-do interrupt setup.
Eric Joyner ixl: Remove VFLR task setup from legacy flow.
Eric Joyner ixl: Shutdown/setup HMC when handling an EMPR reset.

Differential Revision: https://reviews.freebsd.org/D6211
Reviewed by: sbruno, kmacy, jeffrey.e.pieper@intel.com
MFC after: 2 weeks
Sponsored by: Intel Corporation