Drain pending UDP traffic before snapshotting INIT validation state

tests/test_etcp_init_liveness.c

@@ -223,6 +223,12 @@ static void send_init_request_body(const struct ETCP_INIT_REQUEST_PKT *request,
 
 static void request_boundaries(unsigned established) {
     setup(0, established);
+    unsigned drained = 0; uint8_t pending;
+    while (recv(ep[1].socket->fd, (char*)&pending, 1, MSG_PEEK) >= 0) {
+        etcp_connections_read_callback_socket(ep[1].socket->fd, ep[1].socket); drained++;
+    }
+    CHECK(socket_get_error() == ERR_WOULDBLOCK || socket_get_error() == ERR_AGAIN);
+    DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "INIT boundary fixture: established=%u drained_previous_packets=%u", established, drained);
     struct ETCP_INIT_REQUEST_PKT request = {0};
     for (unsigned i = 0; i < 8; i++) {
         request.node_id[i] = ep[0].inst->node_id >> (56 - i * 8);
@@ -362,11 +368,11 @@ static void check_memory(size_t baseline) {
 int main(void) {
     debug_config_init(); debug_set_level(DEBUG_LEVEL_ERROR);
     debug_set_category_level(DEBUG_CATEGORY_CRYPTO, DEBUG_LEVEL_DISABLED);
+    test_clock_init(10); CHECK(socket_platform_init() == 0);
     if (getenv("UTUN_TEST_DEBUG")) {
         debug_set_category_level(DEBUG_CATEGORY_ETCP, DEBUG_LEVEL_DEBUG);
         debug_set_category_level(DEBUG_CATEGORY_DEBUG, DEBUG_LEVEL_DEBUG);
     }
-    test_clock_init(10); CHECK(socket_platform_init() == 0);
     size_t baseline = u_get_allocated_count();
     for (unsigned established = 0; established < 2; established++) { request_boundaries(established); check_memory(baseline); }
     response_boundaries(); check_memory(baseline);