Added RX and TX active times in PHY statistics (ARMmbed#2255)

Author: Jarkko Paso

nanostack/platform/arm_hal_phy.h

@@ -192,6 +192,8 @@ typedef struct phy_rf_statistics_s {
     uint32_t crc_fails;        ///< CRC failures
     uint32_t tx_timeouts;      ///< transmission timeouts
     uint32_t rx_timeouts;      ///< reception timeouts
+    uint64_t tx_active_time;   ///< transmission active time
+    uint64_t rx_active_time;   ///< reception active time
 } phy_rf_statistics_s;
 
 /** Virtual data request */