Bluetooth: Host: Fix resolvable address update with Ext Adv enabled

Fix resolvable address update after RPA timeout with
Extended Advertising support enabled. As Extended
Advertising HCI Commands are being used to start legacy
advertising, incorrectly the local random address was being
used instead of using the random address populated in the
Extended Advertising set. BT_DEV_RPA_VALID is not cleared
when Extended Advertising HCI commands are used, hence the
local random address is not updated and the incorrect use
of it did not make any change to the advertising when
disabled and enabled at RPA timeout.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>