package/busybox: fix avahi-autoipd error message

When using a combination of udhcpc and avahi-autoipd in case of receiving IP
from a DHCP server, the following message can be seen:
"Failed to kill daemon: No such file or directory".
Add a check for a running avahi-autoipd to fix this issue.

Signed-off-by: Lukasz Tekieli <tekieli.lukasz@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>