examples: every socket thread needs a msg queue

examples/posix_sockets/main.c

@@ -20,9 +20,11 @@
 
 #include <stdio.h>
 
+#include "msg.h"
 #include "shell.h"
 
-#define MAIN_MSG_QUEUE_SIZE (1)
+#define MAIN_MSG_QUEUE_SIZE (4)
+static msg_t main_msg_queue[MAIN_MSG_QUEUE_SIZE];
 
 extern int udp_cmd(int argc, char **argv);
 
@@ -33,6 +35,9 @@ static const shell_command_t shell_commands[] = {
 
 int main(void)
 {
+    /* a sendto() call performs an implicit bind(), hence, a message queue is
+     * required for the thread executing the shell */
+    msg_init_queue(main_msg_queue, MAIN_MSG_QUEUE_SIZE);
     puts("RIOT socket example application");
     /* start shell */
     puts("All up, running the shell now");