fix: adapt tests and fix bugs from enhancements rebase onto main

- Fix transport_tcp.c: initialize server->ssl_ctx to NULL
  (prevents SSL_CTX_free on garbage when server_create_tls fails)
- Fix test_transport_tcp.c: client_create now sets fd=-1, family=AF_UNSPEC
- Fix test_transport_tcp.c: server address family may be AF_INET or AF_INET6
- Fix test_file_sendfile.c: send_path=false protocol includes file_type prefix

tests/test_file.c

@@ -217,6 +217,10 @@ static void test_file_send_no_path() {
   pid_t pid = fork();
   if (pid == 0) {
     close(p[1]);
+    // Read file type indicator
+    int file_type;
+    EXPECT_TRUE(receive_int(p[0], &file_type));
+    EXPECT_EQ_INT(file_type, (int)FILE_TYPE_REGULAR);
     Data* received = receive_data(p[0]);
     close(p[0]);