rndis_wlan: workaround device not returning bss for currently connected AP

BCM4320a devices do not return bss for currently connected AP in bss-list,
althought this is required by NDIS specs. Missing bss leads to warning at
net/wireless/sme.c:__cfg80211_connect_result(), WARN_ON(!bss).

Workaround this by crafting bss manually with information we can read from
device. Workaround is only used when device bss-list does not return current
bss, and so is only used with BCM4320a devices and not newer BCM4320b ones.

Fixes bug #20152.

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