olsrd: fix olsrd starting before network

olsrd: fix olsrd starting before network

Should fix #691.

Sometimes the wifi interface is not ready before olsrd tries to access
it. This leads to warnings in the form of:

daemon.info olsrd: /etc/rc.d/S65olsrd: olsrd_write_interface()
	Warning: Interface 'wireless0' not found, skipped
daemon.notice procd: /etc/rc.d/S65olsrd: olsrd: /etc/rc.d/S65olsrd:
	olsrd_write_interface() Warning: Interface 'wireless0' not found,			skipped

We make use of the "wait_for" procd command that allows us to wait for
the network before starting olsrd.

Tested-by: Noki
Signed-off-by: Nick Hainke <vincent@systemli.org>