/usr/share/aide/config/aide/aide.conf.d/31_aide_ifplugd is in aide-common 0.16~a2.git20130520-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | @@define INTERFACES eth0
/@@{RUN}/ifplugd\.@@{INTERFACES}\.pid$ VarFile
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