nl80211: announce radios/interfaces when switching namespaces

When a wiphy changes its namespace, all interfaces are moved to the
new namespace as well. The network interfaces are properly announced
as leaving on the old and as appearing on the new namespace through
RTM_NEWLINK/RTM_DELLINK. On nl80211, however, these events are missing
for radios and their interfaces.

Add netlink announcements through nl80211 when switching namespaces,
so userspace can rely on these events to discover radios properly.

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