datapath-windows: return netlink error for read operation

datapath-windows: return netlink error for read operation

The kernel datapath returns a NL error message upon any errors
during read operations, and returns STATUS_SUCCESS as the return
code. We reply on the input NL request to get the family ID, and the
PID. However, when the request is of type OVS_CTRL_CMD_EVENT_NOTIFY
and OVS_CTRL_CMD_READ_NOTIFY, there's no input buffer associated
with the request. So, we use a temporary input buffer to be able to
call the Netlink APIs for constructing the output NL error message.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Acked-by: Sairam Venugopal <vsairam@vmware.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>