make tcp_server_posix_test pass on foundry

test/core/iomgr/tcp_server_posix_test.cc

@@ -439,6 +439,11 @@ int main(int argc, char** argv) {
       static_cast<test_addrs*>(gpr_zalloc(sizeof(*dst_addrs)));
   grpc::testing::TestEnvironment env(argc, argv);
   grpc_init();
+  // wait a few seconds to make sure IPv6 link-local addresses can be bound
+  // if we are running under docker container that has just started.
+  // See https://github.com/moby/moby/issues/38491
+  // See https://github.com/grpc/grpc/issues/15610
+  gpr_sleep_until(grpc_timeout_seconds_to_deadline(4));
   {
     grpc_core::ExecCtx exec_ctx;
     g_pollset = static_cast<grpc_pollset*>(gpr_zalloc(grpc_pollset_size()));