Bluetooth: Queue incoming ACL data until BT_CONNECTED state is reached

This patch adds a queue for incoming L2CAP data that's received before
l2cap_connect_cfm is called and processes the data once
l2cap_connect_cfm is called. This way we ensure that we have e.g. all
remote features before processing L2CAP signaling data (which is very
important for making the correct security decisions).

The processing of the pending rx data needs to be done through
queue_work since unlike l2cap_recv_acldata, l2cap_connect_cfm is called
with the hci_dev lock held which could cause potential deadlocks.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>