cfg80211: allow wext to remove keys that don't exist

Some applications using wireless extensions expect to be able to
remove a key that doesn't exist. One example is wpa_supplicant
which doesn't actually change behaviour when running into an
error while trying to do that, but it prints an error message
which users interpret as wpa_supplicant having problems.

The safe thing to do is not change the behaviour of wireless
extensions any more, so when the driver reports -ENOENT let
the wext bridge code return success to userspace. To guarantee
this, also document that drivers should return -ENOENT when the
key doesn't exist.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/cfg80211.h

@@ -781,10 +781,11 @@ enum wiphy_params_flags {
  * @get_key: get information about the key with the given parameters.
  *	@mac_addr will be %NULL when requesting information for a group
  *	key. All pointers given to the @callback function need not be valid
- *	after it returns.
+ *	after it returns. This function should return an error if it is
+ *	not possible to retrieve the key, -ENOENT if it doesn't exist.
  *
  * @del_key: remove a key given the @mac_addr (%NULL for a group key)
- *	and @key_index
+ *	and @key_index, return -ENOENT if the key doesn't exist.
  *
  * @set_default_key: set the default key on an interface
  *