[FINAL] A-MPDU extension

[Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>]

Since there haven't been any objections to the A-MPDU proposal, here's a
repost of the normative text for the A-MPDU field. I'll make the wiki
changes next week and will post the patches to the relevant projects.

--- begin description ---

Bit Number: 20
Structure: u32 reference number,
           u16 flags,
           u8 delimiter CRC value,
           u8 reserved
Required Alignment: 4 bytes

The presence of this field indicates that the frame was received as part
of an a-MPDU.

The reference number is generated by the capture device and is the same
across each subframe of an A-MPDU. Since the capture device might be
capable of capturing multiple channels or data from multiple
(concurrent) captures could be merged, the reference number is not
guaranteed to be unique across different channels. As a result,
applications should use the channel information together with the
reference number to identify the subframes belonging to the same A-MPDU.

The following flags are defined:

0x0001: driver reports 0-length subframes
0x0002: frame is 0-length subframe (valid only if 0x0001 is set)
0x0004: last subframe is known (should be set for all subframes in an
        A-MPDU)
0x0008: this frame is the last subframe
0x0010: delimiter CRC error
0x0020: delimiter CRC value known: the delimiter CRC value field is
        valid
0xffc0: reserved

Within an A-MPDU, the subframe index can be determined by the
application so it is not included, but depending on the driver reporting
this may miss 0-length subframes.

--- end of description ---

johannes