ppp: release rtnl mutex when interface creation fails

Add missing rtnl_unlock() in the error path of ppp_create_interface().

Fixes: 58a89eca ("ppp: fix lockdep splat in ppp_dev_uninit()")
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp/ppp_generic.c

@@ -2816,6 +2816,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
 
 out2:
 	mutex_unlock(&pn->all_ppp_mutex);
+	rtnl_unlock();
 	free_netdev(dev);
 out1:
 	*retp = ret;