4kn and biosdisk.c

[Toomas Soome]

hi!

if you have 4kn disks and BIOS capable of 4k IO with INT13, could you please test https://reviews.freebsd.org/D11174 <https://reviews.freebsd.org/D11174> and give some feedback:)

The patch itself has been in use for some time in illumos. PS: as noted in test plan, this only can be tested by loader now and not by earlier stages (lsdev, lszfs, ls device:path commands).

thanks,
toomas