[NETFILTER]: nf_conntrack_netbios_ns: fix uninitialized member in expectation

->helper is uninitialized in the expectation registered by the netbios_ns
helper and it later copied to the expected connection, which causes invalid
memory dereferences when trying to call the helper.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/nf_conntrack_netbios_ns.c b/net/netfilter/nf_conntrack_netbios_ns.c
index a5b234e..2a48efd 100644
--- a/net/netfilter/nf_conntrack_netbios_ns.c
+++ b/net/netfilter/nf_conntrack_netbios_ns.c
@@ -89,6 +89,7 @@
 
 	exp->expectfn             = NULL;
 	exp->flags                = NF_CT_EXPECT_PERMANENT;
+	exp->helper               = NULL;
 
 	nf_conntrack_expect_related(exp);
 	nf_conntrack_expect_put(exp);