zebra: Move clear_nhlfe_installed to calling functions

zebra: Move clear_nhlfe_installed to calling functions

The function clear_nhlfe_installed is to be called
when we get a install failure of some sort for
a lsp change.  Since an install failure can happen
in both linux and openBSD moving the function call
northbound is a good idea.

I've also added it to the kernel_del_lsp for completeness
on failure as well, even though neither linux or openBSD
currently can fail a uninstall.

This still leaves the hole where if we have multiple
nhlfes and have an install failure we are not quite
doing the right thing by just blanketly calling
clear_nhlfe_installed.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>