batman-adv: Use default throughput value on cfg80211 error

A wifi interface should never be handled like an ethernet devices. The
parser of the cfg80211 output must therefore skip the ethtool code when
cfg80211_get_station returned an error.

Fixes: f44a3ae9 ("batman-adv: refactor wifi interface detection")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Reviewed-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/bat_v_elp.c

@@ -109,7 +109,9 @@ static u32 batadv_v_elp_get_throughput(struct batadv_hardif_neigh_node *neigh)
 			 */
 			return 0;
 		}
-		if (!ret)
+		if (ret)
+			goto default_throughput;
+
 		return sinfo.expected_throughput / 100;
 	}