nl80211: require and validate vendor command policy

Require that each vendor command give a policy of its sub-attributes
in NL80211_ATTR_VENDOR_DATA, and then (stricly) check the contents,
including the NLA_F_NESTED flag that we couldn't check on the outer
layer because there we don't know yet.

It is possible to use VENDOR_CMD_RAW_DATA for raw data, but then no
nested data can be given (NLA_F_NESTED flag must be clear) and the
data is just passed as is to the command.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -457,6 +457,8 @@ static struct wiphy_vendor_command mac80211_hwsim_vendor_commands[] = {
 			  .subcmd = QCA_NL80211_SUBCMD_TEST },
 		.flags = WIPHY_VENDOR_CMD_NEED_NETDEV,
 		.doit = mac80211_hwsim_vendor_cmd_test,
+		.policy = hwsim_vendor_test_policy,
+		.maxattr = QCA_WLAN_VENDOR_ATTR_MAX,
 	}
 };