Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Fix missing err() format string.

Change cc -> bc : "bc" is "busy count", which is the % of time the channel
is considered "busy but not doing any active TX or frame RX."

Just keep in mind that "frame RX" is "decoding what looks like a wifi
signal", not necessarily "frame successfully decoded for this particular
device."

Add a tool to print out min, average and max channel survey information
from the current channel.

There seem to be some occasional issues with the extension channel
counters reporting more than 100% of use. I'll investigate that
soon.