Updated the conntrack based SNAT spec
Updated the conntrack based SNAT spec

1)Added a new HA logic when conntrack mode is selected.
2)Added info about the config parameter to switch NAT mode
3)Added info about a new CLI for displaying the NAPT switch selected for
each router. 

Change-Id: Idd8388276adf8e4bb7974aaa869d04b3a91e09de
Signed-off-by: Aswin Suryanarayanan <245ded2fd329681a343a9940c2cf4910bae21c4f@redhat.com>

opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt