Bluetooth: Add helper function for clearing the discovery filter

The discovery filter allocates memory for its UUID list. So use
a helper function to free it and reset it to default states.

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

diff --cc include/net/bluetooth/hci_core.h
Simple merge

diff --cc net/bluetooth/hci_core.c
Simple merge