mac80211-hwsim: Provide multicast event for HWSIM_CMD_DEL_RADIO

When deleting old radio via HWSIM_CMD_DEL_RADIO then listeners on the
multicast group "config" are informed.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>