nl80211: Fix set_key regression with some drivers

Commit dbd2fd65 added a mechanism for
user space to indicate whether a default key is being configured for
only unicast or only multicast frames instead of all frames. This
commit added a driver capability flag for indicating whether separate
default keys are supported and validation of the set_key command based
on that capability.

However, this single capability flag is not enough to cover possible
difference based on mode (AP/IBSS/STA) and the way this change was
introduced resulted in a regression with drivers that do not indicate
the new capability (i.e.., more or less any non-mac80211 driver using
cfg80211) when using a recent wpa_supplicant snapshot.

Fix the regression by removing the new check which is not strictly
speaking needed. The new separate default key functionality is needed
only for RSN IBSS which has a separate capability indication.

Cc: stable@kernel.org
Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>