You should add:

    syslogd_flags="${syslogd_flags} -a /var/unbound/dev/log"

to /etc/rc.conf.local to create a syslog socket in the unbound chroot.

You may also want to add the following to /etc/rc.local to start unbound
at boot:

	if [ -x ${PREFIX}/sbin/unbound ]; then
		echo -n ' unbound'; ${PREFIX}/sbin/unbound 
	fi