cxgb4: update supported DCB version

- In CXGB4_DCB_STATE_FW_INCOMPLETE state check if the dcb
  version is changed and update the dcb supported version.

- Also, fill the priority code point value for priority
  based flow control.

Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>