samples: net: echo-client: Handle net_buf out-of-mem gracefully

Do not wait forever for network buffers when receiving data.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

samples/net/echo_client/src/echo-client.c

@@ -36,6 +36,8 @@
 
 #define APP_BANNER "Run echo client"
 
+#define BUF_TIMEOUT K_MSEC(100)
+
 /* Generated by http://www.lipsum.com/
  * 3 paragraphs, 176 words, 1230 bytes of Lorem Ipsum
  */
@@ -107,9 +109,10 @@ struct net_pkt *prepare_send_pkt(struct net_app_ctx *ctx,
 {
 	struct net_pkt *send_pkt;
 
-	send_pkt = net_app_get_net_pkt(ctx, AF_UNSPEC, K_FOREVER);
-
-	NET_ASSERT(send_pkt);
+	send_pkt = net_app_get_net_pkt(ctx, AF_UNSPEC, BUF_TIMEOUT);
+	if (!send_pkt) {
+		return NULL;
+	}
 
 	*expecting_len = net_pkt_append(send_pkt, *expecting_len, lorem_ipsum,
 					K_FOREVER);