Restore hapd->interface_added tracking to core hostapd

Restore hapd->interface_added tracking to core hostapd

This reverts parts of commit 390e489c0d9415caf103367136eaa534b559837c
that tried to enable removal of the first BSS. Since that operation is
now forced to remove all BSSs, these changes are not needed. The
hostapd_if_remove() operation in hostapd_free_hapd_data() is problematic
for the first BSS since it ends up freeing driver wrapper information
that is needed later when deinitializing the driver wrapper.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>