vtysh: fix some macro breakage

vtysh: fix some macro breakage

vtysh's extract.pl script doesn't cope with install_element(var, ) where
"var" is not one of the FOO_NODE constants.  Also, the future defun_lex
tool doesn't deal well with preprocessor expansions in the same regard.

This tries simplifying out some of these.  lib/distribute.c needs
further thinking.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>