Bluetooth: Improve fixed channel lookup based on link type

When notifying global fixed channels of new connections it doesn't make
sense to consider channels meant for a different link type than the one
available. This patch adds an extra parameter to the
l2cap_global_fixed_chan() lookup function and ensures that only channels
matching the current hci_conn type are looked up.

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