Blktapctrl compatibility layer

Blktapctrl compatibility layer

I originally had just changed the NEWINTF ioctl to send over 48-bits
of information, which works on 64-bit but not on 32-bit (since the arg
is an unsigned long).  Additionally, the previous changes would break
an older userland against a new kernel.  For that reason, introduce a
new ioctl (NEWINTF_EXT) that fixes both of these problems.  This is
the dom0 userland side.

Signed-off-by: Chris Lalancette <clalance@redhat.com>