Initial implementation for hwvtepsouthbound

Patchset1: Adds basic infra to handle incoming connections

Patchset2: Complete handling of switch initiated connection

Pending Items:
1. Updating data store on switch initiated connections
2. User initiated connections
3. Data Change Listener
4. HTWVTEP Command patterns

Change-Id: Idf6cf40eba53a9c0a18e9081e5ca23c7ab12a90c
Signed-off-by: Vishal Thapar <vishal.thapar@ericsson.com>