babeld: Don't kill -9 on stop

babeld: Don't kill -9 on stop

Killing anything with -9 is a bad idea.  When killed this way, babeld
won't be able to properly disassociate from its neighbours, withdraw its
announced routes or remove routes from the kernel.

This got introduced in bab933d4cad8 ("babeld: Update to version 1.8.3 +
fix init") with an unrelated change.  The purpose of the change is unclear
because stopping and restarting babeld worked fine without this change.

Signed-off-by: Baptiste Jonglez <git@bitsofnetworks.org>