feat(RadioInterface): Tx power gain calculation rework (#6796)

- Rename REGULATORY_GAIN_LORA to TX_GAIN_LORA
- Move gain-based Tx power clamping from RadioInterface::applyModemConfig() to RadioInterface::limitPower()
  - User-configured Tx power now matches the Tx power out of the device connector
- Re-order [LoRa Chip]Interface.cpp limitPower() to take place before the final Tx power clamping so we clamp based on the pre-PA Tx power rather than user-configured Tx power

Tested on XIAO BLE variant.

Signed-off-by: Andrew Yong <me@ndoo.sg>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/LR11x0Interface.cpp

@@ -71,6 +71,8 @@ template <typename T> bool LR11x0Interface<T>::init()
 
     RadioLibInterface::init();
 
+    limitPower();
+
     if (power > LR1110_MAX_POWER) // Clamp power to maximum defined level
         power = LR1110_MAX_POWER;
 
@@ -80,8 +82,6 @@ template <typename T> bool LR11x0Interface<T>::init()
         preambleLength = 12; // 12 is the default for operation above 2GHz
     }
 
-    limitPower();
-
 #ifdef LR11X0_RF_SWITCH_SUBGHZ
     pinMode(LR11X0_RF_SWITCH_SUBGHZ, OUTPUT);
     digitalWrite(LR11X0_RF_SWITCH_SUBGHZ, getFreq() < 1e9 ? HIGH : LOW);