Bluetooth: HCI: Fix tracking of instances sharing handle 0x00

When the controller supports a single advertising set, instance 1 uses
handle 0x00 which is the same handle used by instance 0 (Global
Advertising), but hci_cc_le_set_ext_adv_enable would lookup the instance
using the handle as instance identifier, marking instance 0 as
enabled/disabled instead of instance 1, leaving its state out of sync.

Fix this by matching instances by handle and, for handle 0x00, using
hdev->cur_adv_instance, now set when enabling an instance, to determine
which instance owns the set. Also disable the instance sharing the
advertising set of instance 0 before overriding it.

Fixes: e77f43d531af ("Bluetooth: hci_core: Fix not handling hdev->le_num_of_adv_sets=1")
Assisted-by: OpenCode:claude-opus-5.5
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>