MD-SAL transaction chaining API

This API complements the normal MD-SAL transaction API. Applications can
use this API to maintain inter-transaction ordering and data
consistency.

Change-Id: Ia603f7dacf081fb1528d149f4635c2f22101a7a0
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "MD-SAL transaction chaining API"