Cleaup and formatting fixes for irq allocations

Remove comments for obvious calls.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Point tail_blk_ctl to the first node

Commit d8d5445d moved assignment of tail_blk_ctl to point to the last
allocated node. This is incorrect as it should point to the first
unused node.

wcn36xx_dxe_free_ctl_block needs to be updated to reflect this change.
Simplify it while at it.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Improve TX BD handling

The same BD was used for all TX's. Change this to use a pre-calculated
buffer address in the dxe ctl structure.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Enable TX done IRQs

Generate a TX done IRQ when TX transfer is done.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Return TXed frames to mac80211.

On TX done IRQ reap all transferred skbs.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>