netfilter: conntrack: wrap two inline functions in config checks.

nf_conntrack_synproxy.h contains three inline functions. The contents
of two of them are wrapped in CONFIG_NETFILTER_SYNPROXY checks and just
return NULL if it is not enabled. The third does nothing if they return
NULL, so wrap its contents as well.

nf_ct_timeout_data is only called if CONFIG_NETFILTER_TIMEOUT is
enabled. Wrap its contents in a CONFIG_NETFILTER_TIMEOUT check like the
other inline functions in nf_conntrack_timeout.h.

Signed-off-by: Jeremy Sowden <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/nf_conntrack_synproxy.h

···
 static inline bool nf_ct_add_synproxy(struct nf_conn *ct,
 				      const struct nf_conn *tmpl)
 {
+#if IS_ENABLED(CONFIG_NETFILTER_SYNPROXY)
 	if (tmpl && nfct_synproxy(tmpl)) {
 		if (!nfct_seqadj_ext_add(ct))
 			return false;
···
 		if (!nfct_synproxy_ext_add(ct))
 			return false;
 	}
+#endif
 
 	return true;
 }

include/net/netfilter/nf_conntrack_timeout.h

···
 static inline unsigned int *
 nf_ct_timeout_data(const struct nf_conn_timeout *t)
 {
+#ifdef CONFIG_NF_CONNTRACK_TIMEOUT
 	struct nf_ct_timeout *timeout;
 
 	timeout = rcu_dereference(t->timeout);
···
 		return NULL;
 
 	return (unsigned int *)timeout->data;
+#else
+	return NULL;
+#endif
 }
 
 static inline