We should not add new beacon hints even if the wiphy
is not world roaming. Without this we were always adding
a beacon hint if not world roaming for every non world
roaming wiphy interface.

Tested-by: Ben Greear <greearb@candelatech.com>
Reported-by: Ben Greear <greearb@candelatech.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
[fix locking]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>