wl1271: Add SSID configuration for JOIN in ad-hoc

This patch adds code to extract the SSID from the beacon template used for
ad-hoc. The mac80211 currently does not provide the SSID, so this is a
workaround for that, for now.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>