Steps to reproduce:

1. Run cat /sys/class/net/wlan0/speed
2. The above should return speed in Hz, but tells me cat: /sys/class/net/wlan0/speed: Invalid argument

It seems, for wireless interfaces, speed fails. iwconfig reports speed correctly, but is fetched with iw_get_ext(s, ifname, SIOCGIWRATE, &wrq). I haven't managed to figure out how, but I guess the coding gurus in here might know. So - perhaps better to include that into the agent instead?