mac80211_hwsim: do not omit multicast announce of first added radio

The allocation of hwsim radio identifiers uses a post-increment from 0,
so the first radio has idx 0. This idx is explicitly excluded from
multicast announcements ever since, but it is unclear why.

Drop that idx check and announce the first radio as well. This makes
userspace happy if it relies on these events.

Signed-off-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>