set cntrl bits to indicate whether inner header checksum
needs to be calculated whenever the packet is an encapsulated
packet and enable supported encap features.

Fixes: d0a1299c ("cxgb4: add support for vxlan segmentation offload")
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>