mac80211: call dev_alloc_name before copying name to sdata

This partially reverts 1c5cae81, because
the netdev name is copied into sdata->name, which is used for debugging
messages, for example. Otherwise, we get messages like this:

wlan%d: authenticated

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Jiri Pirko <jpirko@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>