[SX128x] getRssi(false) without packet (#1222)

* Update SX128x.h

* Update SX128x.cpp

src/modules/SX128x/SX128x.cpp

@@ -1253,6 +1253,17 @@ float SX128x::getRSSI() {
   }
 }
 
+float SX128x::getRSSI(bool packet) {
+    if (!packet) {
+        // get instantaneous RSSI value
+        uint8_t data[3] = {0, 0, 0}; // RssiInst, Status, RFU
+        this->mod->SPIreadStream(RADIOLIB_SX128X_CMD_GET_RSSI_INST, data, 3);
+        return ((float)data[0] / (-2.0));
+    } else {
+        return this->getRSSI();
+    }
+}
+
 float SX128x::getSNR() {
   // check active modem
   uint8_t modem = getPacketType();

src/modules/SX128x/SX128x.h

@@ -761,6 +761,13 @@ class SX128x: public PhysicalLayer {
     */
     float getRSSI() override;
 
+    /*!
+      \brief Gets RSSI (Recorded Signal Strength Indicator).
+      \param packet Whether to read last packet RSSI, or the current value.
+      \returns RSSI value in dBm.
+    */
+    float getRSSI(bool packet);
+
     /*!
       \brief Gets SNR (Signal to Noise Ratio) of the last received packet. Only available for LoRa or ranging modem.
       \returns SNR of the last received packet in dB.