If any network interface is in down state (chdev -l enX -a state=down), facter does not report networking::interfaces::enX::ip|mac|mtu for any interfaces. facter --debug shows the following error:
...
DEBUG Facter::Resolvers::Aix::Networking - Could not resolve ip6, got undefined method `[]=' for nil:NilClass at /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/facter/resolvers/aix/networking.rb:51:in `block in populate_with_mtu_and_mac!'
...
DEBUG Facter::Resolvers::Aix::Networking - Could not resolve mac, got undefined method `[]=' for nil:NilClass at /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/facter/resolvers/aix/networking.rb:51:in `block in populate_with_mtu_and_mac!'
...
DEBUG Facter::Resolvers::Aix::Networking - Could not resolve mtu, got undefined method `[]=' for nil:NilClass at /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/facter/resolvers/aix/networking.rb:51:in `block in populate_with_mtu_and_mac!'