bcm27xx_bcm2709: Fix re-running set_hostname script.

This script should only run once when the hostname is set to `OpenWrt`.
This fix was added to the other targets, but was still missing for
bcm27xx_bcm2709.

Author: brocaar

conf/full_raspberrypi_bcm27xx_bcm2709/files/etc/uci-defaults/99_set_hostname

@@ -1,3 +1,7 @@
+if [ "$(uci -q get system.@system[0].hostname)" != "OpenWrt" ]; then
+    exit 0
+fi
+
 GWID_END=""
 
 ip link show eth0