Staging: hv: netvsc: call vmbus_sendpacket_pagebuffer directly

Don't do the interface indirection, it's not needed at all.

Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>