Bluetooth: Restrict blocked device check in l2cap_recv_frame to LE

BR/EDR has the connection request and connection request rejection, but
LE doesn't have anything similar. We still request LE connections to
blocked devices to be disconnected but it's possible that ACL data slips
through before that. The check in l2cap_recv_frame really only needs to
be for LE and not BR/EDR because of this.

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