nimble/ll: Fix not setting TX power in HCI VS command

PHY was not configured to use new TX power immediatelly. This resulted
in new TX power being used only after advertising event ended.

nimble/controller/src/ble_ll_hci_vs.c

@@ -128,6 +128,8 @@ ble_ll_hci_vs_set_tx_power(uint16_t ocf, const uint8_t *cmdbuf, uint8_t cmdlen,
         g_ble_ll_tx_power = ble_phy_txpower_round(cmd->tx_power);
     }
 
+    ble_phy_txpwr_set(g_ble_ll_tx_power);
+
     rsp->tx_power = g_ble_ll_tx_power;
     *rsplen = sizeof(*rsp);