cfg80211: Set WEP ciphers

With iwconfig there is no way to properly set the ciphers when trying to
connect to a WEP SSID. Although mac80211 based drivers dont need it, several
fullmac drivers do.
This patch basically sets the WEP ciphers whenever they're not set at all.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>