rndis_wlan: enable infrastructure before setting random essid

Random essid must be set to turn on radio when not connected. If device is
in ad-hoc mode, this results 'media connect' indications with the random
essid which should be ignored.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>