uio_hv_generic: create send and receive buffers

Map in receive and send buffers for networking in UIO device.
These buffers are special and need to be setup by kernel
API's; userspace can not do it.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>