The exported names were not correct (missing the 'v').
#include <haproxy/listener-t.h>
#include <haproxy/sample-t.h>
-extern struct protocol proto_tcp4;
-extern struct protocol proto_tcp6;
+extern struct protocol proto_tcpv4;
+extern struct protocol proto_tcpv6;
int tcp_bind_socket(int fd, int flags, struct sockaddr_storage *local, struct sockaddr_storage *remote);
int tcp_connect_server(struct connection *conn, int flags);