Bluetooth: Host: Check conn/channel status of L2CAP BR

For BR/EDR L2CAP, if the function bt_l2cap_br_chan_send_cb
instead of bt_l2cap_chan_send is called, the ACL conn and
L2CAP chennel status will not be checked.

Check conn/channel status before sending data in
function bt_l2cap_br_chan_send_cb.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>