qeth: repair SBAL elements calculation

When sending skbs, qeth determines the number of qdio SBAL elements
required. If qeth sends a fragmented skb, the SBAL element number
calculation is wrong, because the fragmented data part is added
twice in qeth_l3_tso_elements(). This patch makes sure fragmented
data is handled in qeth_elements_for_frags() only, while
qeth_l3_tso_elements() starts calculation of qdio SBAL elements just
with the linear data part of the skb.

Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>