Remove extra spaces and tabs
Fix indent
Add get_single_sysctl(), a wrapper to get_sysctl() to make it simple to get value of a single sysctl
Add set_single_sysctl(), a wrapper to set_sysctl() to make it simple to set value of a single sysctl
Fix sysctl name
Convert almost all /sbin/sysctl calls to php functions
Avoid reseting firewall hostname by WAN DHCP. It should fix #3746