debian: Integrate interfaces config with OVS startup script.
Currently, there is an option to use the /etc/network/interfaces
file to configure Open vSwitch bridges and ports. To create and
destroy bridges, one has to manually run the following commands.
ifup --allow=ovs $list_of_bridges
ifdown --allow=ovs $list_of_bridges
This commit will automatically run the above two commands when
the system boots up and shuts down respectively through the
OVS startup script.
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>