isisd: fix spftree_area_del typo causing SEGV

spftree_area_del didn't clear the IPv6 L2 spftree due to a simple typo,
leading to a SEGV on shutdown when the still-armed timer would try to
run an IPv6 L2 SPF calculation with its data free'd already.

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