We try to call free_netvsc_device(net_device) when "net_device" is NULL.
It leads to an Oops.
Fixes: f90251c8a6d0 ('hyperv: Increase the buffer length for netvsc_channel_cb()') Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>