Staging: hv: netvsc: Get rid of the usage of the ext field in struct hv_device

Now, eliminate the usage of ext field in struct  hv_device for netvsc driver.
We do this by registering pointer to struct netvsc_device as the driver
specific data and eliminating the current usage of driver specific data
to save and retrieve the pointer to struct net_device.
Additionally, all access to the driver specific data is through
the vmbus wrapper functions. As part of this cleanup, we also get rid
of some unnecessary debug print statements.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>