netfilter: synproxy: ensure zero is returned on non-error return path

Currently functions nf_synproxy_{ipc4|ipv6}_init return an uninitialized
garbage value in variable ret on a successful return.  Fix this by
returning zero on success.

Addresses-Coverity: ("Uninitialized scalar variable")
Fixes: d7f9b2f1 ("netfilter: synproxy: extract SYNPROXY infrastructure from {ipt, ip6t}_SYNPROXY")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_synproxy_core.c

@@ -798,7 +798,7 @@ int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net)
 	}
 
 	snet->hook_ref4++;
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init);
 
@@ -1223,7 +1223,7 @@ nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net)
 	}
 
 	snet->hook_ref6++;
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init);