Added Tx routine for ULD
- define interface for ULD Tx.

Export routines used for Tx data
- Routines common for data transmit are used by cxgb4 and chcr
  drivers.
- EXPORT routines enable transmit from chcr driver.
Signed-off-by: NAtul Gupta <atul.gupta@chelsio.com>
Signed-off-by: NGanesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>