udhcp.user uci commit only new hostnames

Instead of always committing a provided hostname, only commit new hostnames, where
the new hostname doesn't match the current hostname.

Resolves #442

openwrt/files/etc/udhcpc.user

@@ -22,9 +22,11 @@ case "$1" in
     fi
 
     if [ ! -z "$hostname" ]; then
-      uci set 'system.@system[0].hostname'="$hostname"
-      uci commit
       if [ `echo "$HOSTNAME" | tr '[A-Z]' '[a-z]'` != `echo "$hostname" | tr '[A-Z]' '[a-z]'` ]; then
+        # set new hostname
+        uci set 'system.@system[0].hostname'="$hostname"
+        uci commit
+
         # reload/restart whatever needs the hostname updated
         /etc/init.d/system reload
         service zabbix_agentd restart