Bluetooth: host: Fix undefined references to adv in central only builds

Fix regression is central only builds when CONFIG_BT_PRIVACY and/or
CONFIG_BT_EXT_ADV is enabled, or the functions bt_id_reset or
bt_id_delete is called from application.

This resulted in build error for undefined functions
bt_le_ext_adv_foreach and bt_le_adv_lookup_legacy since the definition
for these functions are now only compiled in when CONFIG_BT_BROADCASTER
has been enabled.

Regression from:
53cea471

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>