igb: remove skb_orphan calls

Remove skb_orphan call from igb driver as it can cause multiple issues due
to the fact that it is calling the desctructor and removing the skb from
the socket prior to transmission.

The call was added to improve performance but did so by allowing the skb to
be removed from the socket which gave the socket more window space to
transmit.  The performance gain is not worth the extra problems that this
kind of workaround can introduce as this could lead to a potential DoS if a
UDP stream decided to monopolize the transmit path.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>