[GSoC Weekly Status #1/2] Add sta, hostap and adhoc mode to wtap wlan simulator

Hello,
I spent two weeks reading documents like ieee80211(9), net80211(9),
vnet(9), mbuf(9), and so on, and reading the most helpful part of "FreeBSD
Device Driver: A Guide For The Intrepid". I also get used to jail(8), in
order to build a wireless testing environment.

I have dug in some code of wtap, and found that it's not easy to combine
the whole things. I also found that in some circumstances (like kldunload),
wtap will crash the kernel because of some bugged code. I'll fix it first,
and then start to implement ad-hoc mode on it.