Fix fwaas v2 configuration doc
Fix fwaas v2 configuration doc

The wrong extension was listed in the admin guide.

Change-Id: Idac3ffb974d904c50b2f7563a475d34865266b59
Closes-bug: #1742450

noironetworks/neutron,noironetworks/neutron,mahak/neutron,openstack/neutron,mahak/neutron,huntxu/neutron,mahak/neutron,openstack/neutron,openstack/neutron,huntxu/neutron