l2tp: don't mask errors in pppol2tp_setsockopt()

pppol2tp_setsockopt() unconditionally overwrites the error value
returned by pppol2tp_tunnel_setsockopt() or
pppol2tp_session_setsockopt(), thus hiding errors from userspace.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -1383,8 +1383,6 @@ static int pppol2tp_setsockopt(struct socket *sock, int level, int optname,
 	} else
 		err = pppol2tp_session_setsockopt(sk, session, optname, val);
 
-	err = 0;
-
 end_put_sess:
 	sock_put(sk);
 end: