sock/udp: work around gnrc_sock_recv() returning early timeout

sock_udp_recv_buf_aux() sometimes will return -ETIMEDOUT before
the given timeout has expired (e.g. 28798µs instead of 160000µs).

This messes with many assumptions and breaks protocols that rely
on the timeout.

Until we have a proper fix, add this workaround.

sys/net/gnrc/sock/udp/gnrc_sock_udp.c

@@ -237,6 +237,16 @@ static bool _accept_remote(const sock_udp_t *sock, const udp_hdr_t *hdr,
     return true;
 }
 
+static uint32_t _now_us(void)
+{
+#ifdef MODULE_ZTIMER_USEC
+    return ztimer_now(ZTIMER_USEC);
+#endif
+#ifdef MODULE_ZTIMER_MSEC
+    return ztimer_now(ZTIMER_MSEC) * US_PER_MS;
+#endif
+}
+
 ssize_t sock_udp_recv_buf_aux(sock_udp_t *sock, void **data, void **buf_ctx,
                               uint32_t timeout, sock_udp_ep_t *remote,
                               sock_udp_aux_rx_t *aux)
@@ -274,7 +284,26 @@ ssize_t sock_udp_recv_buf_aux(sock_udp_t *sock, void **data, void **buf_ctx,
         _aux.rssi = &aux->rssi;
     }
 #endif
-    res = gnrc_sock_recv((gnrc_sock_reg_t *)sock, &pkt, timeout, &tmp, &_aux);
+    unsigned now = _now_us();
+    while (1) {
+        res = gnrc_sock_recv((gnrc_sock_reg_t *)sock, &pkt, timeout, &tmp, &_aux);
+
+        if (res != -ETIMEDOUT) {
+            break;
+        }
+
+        /* HACK: gnrc_sock_recv() sometimes returns -ETIMEDOUT too early */
+        uint32_t time_elapsed = _now_us() - now;
+        if (time_elapsed < (timeout - timeout/10))  {
+            DEBUG("gnrc_sock_udp: timeout happened  %"PRIu32" µs early\n",
+                  timeout - time_elapsed);
+            timeout -= time_elapsed;
+            now = _now_us();
+            continue;
+        }
+        break;
+    }
+
     if (res < 0) {
         return res;
     }