ATT_CHAN() macro as a wrapper to CONTAINER_OF is been used by ATT
internals API wherein the main parameter is pointer to bt_l2cap_chan
object. The macro returns pointer to bt_att context object but
CONTAINER_OF's third parameter determines what member is taken into
account in getting right address. Luckily here this third parameter
"chan" of type bt_l2cap_le_chan got of its own sub-member the "chan" of
type bt_l2cap_chan on first position in structure order. If such order
would change somehow there could be taken wrong address.
Change-Id: I955c2af11e001dac90a1eacc281ff167ceb34fb9
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>