Bluetooth: Fix poll() misbehavior when using BT_DEFER_SETUP

When BT_DEFER_SETUP has been enabled on a Bluetooth socket it keeps
signaling POLLIN all the time. This is a wrong behavior. The POLLIN
should only be signaled if the client socket is in BT_CONNECT2 state
and the parent has been BT_DEFER_SETUP enabled.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>