cfg80211: pass name_assign_type to rdev_add_virtual_intf()

This will expose in /sys whether the ifname of a device is set by
userspace or generated by the kernel. The latter kind (wlanX, etc)
is not deterministic, so userspace needs to rename these devices
to names that are guaranteed to stay the same between reboots. The
former, however should never be renamed, so userspace needs to be
able to reliably tell the difference.

Similar functionality was introduced for the rtnetlink core in
commit 5517750f ("net: rtnetlink - make create_link take name_assign_type")

Signed-off-by: Tom Gundersen <teg@jklm.no>
Cc: Kalle Valo <kvalo@qca.qualcomm.com>
Cc: Brett Rudley <brudley@broadcom.com>
Cc: Arend van Spriel <arend@broadcom.com>
Cc: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Cc: Hante Meuleman <meuleman@broadcom.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
[reformat changelog to fit 72 cols]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>