Including sock_inet.h without receiver-t.h causes build failures due to
struct receiver not being defined. Let's just forward-declare it.
extern struct proto_fam proto_fam_inet4;
extern struct proto_fam proto_fam_inet6;
+/* extrenal types */
+struct receiver;
+
int sock_inet4_addrcmp(const struct sockaddr_storage *a, const struct sockaddr_storage *b);
int sock_inet6_addrcmp(const struct sockaddr_storage *a, const struct sockaddr_storage *b);
void sock_inet_set_port(struct sockaddr_storage *addr, int port);