In /etc/rkhunter.conf, normally arguments that are allowed to be
wildcards are documented as such.  Reading the source, ALLOWPROMISCIF
is interpreted as a regular expression, but nothing mentions that it
is a RE.

Perhaps wording in /etc/rkhunter.conf could be (there's no precedent
for REs mentioned in /etc/rkhunter.conf, and a quick look through the
source tells me everything else is either literal or glob):

#
# Allow the specified network interfaces to be in promiscuous mode.
#
# This is a space-separated list of interface names, specified as
# regular expressions as interpreted by awk. The option may be
# specified more than once.
#
# The default value is the null string.
#