Below is the planned commit message:
```
For TSF and beacon generation, each STA have to start its local TSF timer
when it has reach the state IEEE80211_S_RUN, and beacon frames is sended
by the STA has larest TSF timer (oldest STA) in an IBSS.
TSF timer is keeped in HAL of wtap, it’s wroking by continuously updating its
value on timer interupt which is simulated via callout_reset().
For IBSS merge, the STA with smaller TSF timer (younger STA) will be merged
into the IBSS which is owned by a STA with larger TSF timer (older STA). After
merging process, the younger STA will be in the IBSS created by older STA, and
have the BSSID of the this IBSS.
After being merged into other IBSS, the STA stops sending beacon frames.
```
This diff depends on D35752.