[libfko] Have 'make install' run ldconfig if basic fwknop/fwknopd -h exec fails

This commit makes sure that if running 'fwknop -h' or 'fwknopd -h' appears to
fail then run ldconfig under the 'make install' step.  George Herlin reported
that on some systems ldconfig was not automatically getting executed via the
autoconf Makefile config, and since fwknop/fwknopd depend on a shared library
(libfko), ldconfig needs to be executed by 'make install' if it wasn't already
done.