Revert "net: core: maybe return -EEXIST in __dev_alloc_name"

This reverts commit d6f295e9; some userspace (in the case
we noticed it's wpa_supplicant), is relying on the current
error code to determine that a fixed name interface already
exists.
Reported-by: NJouni Malinen <j@w1.fi>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1106,7 +1106,7 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
 	 * when the name is long and there isn't enough space left
 	 * for the digits, or if all bits are used.
 	 */
-	return p ? -ENFILE : -EEXIST;
+	return -ENFILE;
 }
 
 static int dev_alloc_name_ns(struct net *net,