Make ipmi whitelist optional

Not all users of ipmid want to use the whitelist. Or they want to have
their own that behaves differently. This change makes it so one can
disable the built-in whitelist so that OEMs can substitute their own
custom filtering or use none at all.

To disable the whitelist, pass --disable-ipmi-whitelist to configure.
This can be done in Yocto via a bbappend for phosphor-ipmi-host:

EXTRA_OECONF_append = " --disable-ipmi-whitelist"

Tested: Built with and without the whitelist enabled to ensure that the
        whitelist is present when expected to be.

Change-Id: I63f317b6c29ca73cc3296bb2fe38f836004ec35d
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/configure.ac b/configure.ac
index 296165f..29f58e2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -255,6 +255,17 @@
       )
 AM_CONDITIONAL([FEATURE_TRANSPORT_OEM], [test x$transport_oem = xtrue])
 
+# IPMI whitelist mechanism is not needed by everyone; offer a way to disable it
+AC_ARG_ENABLE([ipmi-whitelist],
+    [ --enable-ipmi-whitelist   Enable/disable IPMI whitelist filtering],
+    [case "${enableval}" in
+      yes) ipmi_whitelist=true ;;
+      no) ipmi_whitelist=false ;;
+      *) AC_MSG_ERROR([bad value ${enableval} for --enable-ipmi-whitelist]) ;;
+      esac],[ipmi_whitelist=true]
+      )
+AM_CONDITIONAL([FEATURE_IPMI_WHITELIST], [test x$ipmi_whitelist = xtrue])
+
 # Create configured output
 AC_CONFIG_FILES([
     Makefile