Send and recv all data when necessary

Expose net_recv_all() and net_send_all(), equivalent of net_recv() and
net_send(), but that waits/retries until the requested length has been
transferred.

Use these new functions where it was (wrongly) assumed that the
requested length had been transferred.

app/src/device.c

@@ -3,7 +3,7 @@
 
 SDL_bool device_read_info(socket_t device_socket, char *device_name, struct size *size) {
     unsigned char buf[DEVICE_NAME_FIELD_LENGTH + 4];
-    int r = net_recv(device_socket, buf, sizeof(buf));
+    int r = net_recv_all(device_socket, buf, sizeof(buf));
     if (r < DEVICE_NAME_FIELD_LENGTH + 4) {
         LOGE("Could not retrieve device information");
         return SDL_FALSE;