cxgb4: copy the length of cpl_tx_pkt_core to fw_wr

cxgb4: copy the length of cpl_tx_pkt_core to fw_wr

immdlen field of FW_ETH_TX_PKT_WR is filled in a wrong way,
we must copy the length of all the cpls encapsulated in fw
work request. In the xmit path we missed adding the length
of CPL_TX_PKT_CORE but we added the length of WR_HDR and it
worked because WR_HDR and CPL_TX_PKT_CORE are of same length.
Add the length of cpl_tx_pkt_core not WR_HDR's. This also
fixes the lso cpl errors for udp tunnels

Fixes: 1117bf0cde47 ("cxgb4: add support for vxlan segmentation offload")
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>