Here is the answer : I couldn't find this value of 7981 bytes anywhere, and the links on wikipedia were dead, so I edited it to 2304.
The maximum 802.11 MTU is 2304 bytes.
Here are the different possible maximum frame size of a 802.11 packet, according to the encryption scheme in use :
MTU + MAC Header + Encryption Header
- WEP : 2304 + 34 + 8 = 2346 bytes
- WPA (TKIP) : 2304 + 34 + 20 = 2358 bytes
- WPA2 (CCMP) : 2304 + 34 + 16 = 2354 bytes
If QoS is used, an additional 2 bytes header is added before the payload, increasing the frame size by 2 bytes.
Note that the Encryption header is missing on the picture. It would be placed after QoS Control, inside the frame body, but would not decrease the available 2304 bytes for application data.
In addition, the "Address 4" field of a 802.11 frame is often not used, effectively reducing the frame size by 6 bytes for most 802.11 MPDU.