Added support for FreeBSD and pfSense

Hi Stefan. Thanks for sharing ledctl_6501. This is very useful for controlling the LEDs on my net6501. I run a net6501 as a router using pfSense 2.1. I took your source and added support for the FreeBSD OS, including pfSense. I have verified that the source still compiles on Linux. I would like to contribute these changes to your repository if you agree with them.