Added TX/RX bytes in PHY statistics (#2281)

Author: Jarkko Paso

nanostack/platform/arm_hal_phy.h

@@ -195,6 +195,8 @@ typedef struct phy_rf_statistics_s {
     uint32_t rx_timeouts;      ///< reception timeouts
     uint64_t tx_active_time;   ///< transmission active time
     uint64_t rx_active_time;   ///< reception active time
+    uint32_t tx_bytes;         ///< transmitted bytes
+    uint32_t rx_bytes;         ///< received bytes
 } phy_rf_statistics_s;
 
 /** Virtual data request */