net: Fix potential uninitialized use of variables in net_bind()

If the list of addrinfos give to net_bind() contains only IPv4 or only
IPv6 addresses, then the ipv4 and ipv6 variables may be used uninitialized.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/net/net.c

@@ -204,7 +204,8 @@ fail:
 
 int net_bind(const struct addrinfo *addrinfo, int fds[2])
 {
-	const struct addrinfo *ipv6, *ipv4;
+	const struct addrinfo *ipv6 = NULL;
+	const struct addrinfo *ipv4 = NULL;
 	unsigned int num;
 
 	if (addrinfo->ai_family == AF_INET)