cxgb4vf: fix some errors in Gather List to skb conversion

There were some errors in the way that internal Gather Lists were being
translated into skb's.  This also makes the VF Driver look more like the PF
Driver to facilitate easier comarison.

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>