ath6kl: don't share channel data between interfaces

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
ath6kl: free aggr_conn in same file as allocation

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
ath6kl: add softmac capability

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>