nimble/phy: Fix receiver configuration on late RX

If we are late when scheduling RX, receiver is enabled anyway since we
may just want to scan for "anything". However, current code only enables
receiver but does not configure it so the results seem unpredictable.

This patch fixes this by ensuring that radio is properly configured for
RX in both cases.

X-Original-Commit: 068c09a8da97bc62eddd5084fa1e40f910abf7e8

nimble/drivers/nrf52/src/ble_phy.c

@@ -1443,6 +1443,7 @@ ble_phy_tx_set_start_time(uint32_t cputime, uint8_t rem_usecs)
 int
 ble_phy_rx_set_start_time(uint32_t cputime, uint8_t rem_usecs)
 {
+    bool late = false;
     int rc = 0;
 
     /* XXX: This should not be necessary, but paranoia is good! */
@@ -1451,16 +1452,29 @@ ble_phy_rx_set_start_time(uint32_t cputime, uint8_t rem_usecs)
 
     if (ble_phy_set_start_time(cputime, rem_usecs, false) != 0) {
         STATS_INC(ble_phy_stats, rx_late);
+
+        /*
+         * Disable PPI so ble_phy_rx() will start RX immediately after
+         * configuring receiver.
+         */
         NRF_PPI->CHENCLR = PPI_CHEN_CH21_Msk;
-        NRF_RADIO->TASKS_RXEN = 1;
-        rc = BLE_PHY_ERR_RX_LATE;
+        late = true;
     } else {
         /* Enable PPI to automatically start RXEN */
         NRF_PPI->CHENSET = PPI_CHEN_CH21_Msk;
-
-        /* Start rx */
-        rc = ble_phy_rx();
     }
+
+    /* Start rx */
+    rc = ble_phy_rx();
+
+    /*
+     * If we enabled receiver but were late, let's return proper error code so
+     * caller can handle this.
+     */
+    if (!rc && late) {
+        rc = BLE_PHY_ERR_RX_LATE;
+    }
+
     return rc;
 }