Add support to set nRF24l01 LNA gain

[BLLuis]

Implementing a channel scanner and due to the lack of nRF24l01 signal meter I turn off the LNA to reduce in 1.5 db signal sensitivity getting at least 3 levels for signal strength.
The library don't have a function to set LNA or sensitivity so I'm using RADIOLIB_GODMODE and RADIOLIB_LOW_LEVEL to have acces to Module pointer using getMod and writting to nRF24 to change this setting.

These are some lines of my code as example:

`

#define RADIOLIB_NRF24_RF_LNA_OFF                           0b00000000  //  0     0   LNA gain: Off
#define RADIOLIB_NRF24_RF_LNA_ON                            0b00000001  //  0     0             On

/*
getMod is available defining

#define RADIOLIB_GODMODE    (1)
#define RADIOLIB_LOW_LEVEL  (1)

in component/src/BuildOptUser.h file
*/

Module * pModuleRadio0 = m_pRadio0->getMod();
radioState = pModuleRadio0->SPIsetRegValue(RADIOLIB_NRF24_REG_RF_SETUP, RADIOLIB_NRF24_RF_LNA_ON, 0, 0);

`

This is good not only to reduce sensitivity but also to reduce current consumption in 0.8ma, my code is not tested on a real device yet.
Wish to see this in the library to avoid using God mode.