rc: fix drop-in script execution

src/etc/rc.opnsense

 #!/bin/sh
 
-if [ ! -f /etc/rc.conf -o -z "$(ls /etc/rc.conf.d)" ]; then
-	exit 0
-fi
-
 # check which services to enable
-. /etc/rc.conf
-for rc_conf in /etc/rc.conf.d/*;
-do
-	. $rc_conf
+if [ -f /etc/rc.conf ]; then
+	. /etc/rc.conf
+fi
+for RC_CONF in $(ls /etc/rc.conf.d); do
+	. /etc/rc.conf.d/${RC_CONF}
 done
 
 # probe all deamons in /usr/local/etc/rc.d/