The conf doesn't contain any basic rates in some cases. Most notably,
when starting a P2P GO in 5 GHz. Use the iface rates which are
initialized in hostapd_prepare_rates() to the conf rates or set to
default values if no conf values exist. This fixes a bug introduced in
commit e5693c4775bae65faa960f80889f98b0a6cb2e1c.
Signed-hostap: Arik Nemtsov <arik@wizery.com>