Pull xen block changes from Konrad:
Two fixes, both of them spotted by Amazon:
1) Fix in Xen-blkfront caused by the re-write in 4.8 time-frame.
2) Fix in the xen_biovec_phys_mergeable which allowed guest
requests when using NVMe - to slurp up more data than allowed
leading to an XSA (which has been made public today).