mac80211_hwsim: fix module init error paths for netlink

There is no unregister netlink notifier and family on error paths
in init_mac80211_hwsim(). Also there is an error path where
hwsim_class is not destroyed.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: 62759361

 ("mac80211-hwsim: Provide multicast event for HWSIM_CMD_NEW_RADIO")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>