netfilter: xt_TCPMSS: correct return value in tcpmss_mangle_packet

In commit b396966c (netfilter: xt_TCPMSS: Fix missing fragmentation handling),
I attempted to add safe fragment handling to xt_TCPMSS.  However, Andy Padavan
of Project N56U correctly points out that returning XT_CONTINUE in this
function does not work.  The callers (tcpmss_tg[46]) expect to receive a value
of 0 in order to return XT_CONTINUE.
Signed-off-by: NPhil Oester <kernel@linuxace.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_TCPMSS.c

@@ -60,7 +60,7 @@ tcpmss_mangle_packet(struct sk_buff *skb,
 
 	/* This is a fragment, no TCP header is available */
 	if (par->fragoff != 0)
-		return XT_CONTINUE;
+		return 0;
 
 	if (!skb_make_writable(skb, skb->len))
 		return -1;