ovs-monitor-ipsec: Detect correctly IPSEC configuration changes

ovs-monitor-ipsec: Detect correctly IPSEC configuration changes

If Open vSwitch has IPSEC tunnel (with certificates) and Interface
table was updated, then ovs-monitor-ipsec daemon would incorrectly
remove and readd all existing IPSEC tunnels.

The root cause for this issue was that "peer_cert_file" key was present in
interfaces dictionary, but it was not present in new_interfaces dictionary.

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Reported-by: Niklas Andersson <nandersson@nicira.com>