bhyve nvme: Implement Log Page Offset

Modify the Get Log Page command to parse the Log Page Offset fields to
support more recent versions of the NVMe specification.

Fixes various tests for UNH Test 1.3.*

Reviewed by: imp, allanjude
Tested by: jason@tubnor.net
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D33568