Add timeout send/recv and multicast client/server socket examples (#1519)

Add a couple of socket examples that can be used with WAMR:
- The `timeout_client` and `timeout_server` examples demonstrate socket
  send and receive timeouts using the socket options
- The `multicast_client` and `multicast_server` examples demonstrate receiving
  multicast packets in WASM

And add several macro controls for `socket_opts` example.

samples/socket-api/wasm-src/timeout_client.c

@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2022 Amazon.com Inc. or its affiliates. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <unistd.h>
+#ifdef __wasi__
+#include <wasi_socket_ext.h>
+#endif
+
+int
+main(int argc, char *argv[])
+{
+    int socket_fd;
+    struct sockaddr_in addr;
+    struct timeval tv = { 0, 1 };
+    const int snd_buf_len = 8;
+    const int data_buf_len = 1000000;
+    char *buffer = (char *)malloc(sizeof(char) * data_buf_len);
+    int result;
+    socklen_t opt_len = sizeof(snd_buf_len);
+    struct timeval snd_start_time, snd_end_time;
+    int bool_opt = 1;
+
+    if (buffer == NULL) {
+        perror("Allocation failed, please re-run with larger heap size");
+        return EXIT_FAILURE;
+    }
+
+    /* 127.0.0.1:1234 */
+    addr.sin_family = AF_INET;
+    addr.sin_port = htons(1234);
+    addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+
+    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
+        perror("Create socket failed");
+        goto fail1;
+    }
+
+    if (setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &bool_opt,
+                   sizeof(bool_opt))
+        == -1) {
+        perror("Failed setting SO_REUSEADDR");
+        goto fail2;
+    }
+
+    if (setsockopt(socket_fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) == -1) {
+        perror("Failed setting SO_RCVTIMEO");
+        goto fail2;
+    }
+
+    if (setsockopt(socket_fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)) == -1) {
+        perror("Failed setting SO_SNDTIMEO");
+        goto fail2;
+    }
+
+    if (setsockopt(socket_fd, SOL_SOCKET, SO_SNDBUF, &data_buf_len,
+                   sizeof(data_buf_len))
+        == -1) {
+        perror("Failed setting SO_SNDBUF");
+        goto fail2;
+    }
+
+    if (connect(socket_fd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
+        perror("Connect failed");
+        goto fail2;
+    }
+
+    if (getsockopt(socket_fd, SOL_SOCKET, SO_SNDBUF, (void *)&data_buf_len,
+                   &opt_len)
+        == -1) {
+        perror("Failed getting SO_SNDBUF");
+        goto fail2;
+    }
+
+    printf("Waiting on recv, which should timeout\n");
+    result = recv(socket_fd, buffer, 1, 0);
+
+    if (result != -1 || errno != EAGAIN) {
+        perror("Recv did not timeout as expected");
+        goto fail2;
+    }
+
+    printf("Waiting on send, which should timeout\n");
+    gettimeofday(&snd_start_time, NULL);
+    result = send(socket_fd, buffer, data_buf_len, 0);
+    gettimeofday(&snd_end_time, NULL);
+
+    if (result >= data_buf_len
+        || snd_start_time.tv_sec != snd_end_time.tv_sec) {
+        perror("Send did not timeout as expected");
+        goto fail2;
+    }
+
+    printf("Success. Closing socket \n");
+    close(socket_fd);
+    free(buffer);
+    return EXIT_SUCCESS;
+
+fail2:
+    close(socket_fd);
+fail1:
+    free(buffer);
+    return EXIT_FAILURE;
+}