Bluetooth: Add channel parameter to mgmt_pending_find() API

To be able to have pending commands for different HCI channels we need
to be able to distinguish for which channel a command was sent to. The
channel information is already part of the socket data and can be
fetched using the recently added hci_sock_get_channel() function. To not
require all mgmt.c code to pass an extra channel parameter this patch
also adds a helper pending_find() & pending_find_data() functions which
act as a wrapper to the new mgmt_pending_find() & mgmt_pending_find_data()
APIs.

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