staging: unisys: visornic: enable skb->len error-check, remove DEBUG blocks

* A skb->len error-check was enabled (removed from a "#ifdef DEBUG" block).
* Several unneeded "#ifdef DEBUG" blocks were removed.
* A dev_err() was converted to the more-appropriate netdev_err().

Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>