ixl/iavf: Update ixl(4) and iavf(4) [previously ixlv] man pages

Since there have been major updates to both drivers in r339338,
refresh the man pages with new and updated information.

Reviewed by: sbruno@, 0mp@, jeffrey.e.pieper@intel.com, manpages
Approved by: re (gjb@, kib@)
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D15927