neutron-api config-flags max_allowed_address_pair

[Juan Pablo Vargas Soruco]

I needed to change neutron-api config-flags to increase the max_allowed_address_pair quota to be able to do nested virtualization and be able to have more than 10 KVM virtual machines with different IP Address and MACs.

Just opening the bug following the warning.

WARNING: this is not the recommended way to configure the underlying services that this charm installs and is used at the user's own risk. This option is mainly provided as a stop-gap for users that either want to test the effect of modifying some config or who have found a critical bug in the way the charm has configured their services and need it fixed immediately. We ask that whenever this is used, that the user consider opening a bug on this charm at