Virtio modern has the common data organized in little endian, but
on powerpc64 BE it was reading and writing in the wrong endian.
Submitted by: Leonardo Bianconi <leonardo.bianconi@eldorado.org.br>
Reviewed by: bryanv, alfredo
Sponsored by: Eldorado Research Institute (eldorado.org.br)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D28947