Lora: Remove duplicate LinkCheckReq MAC command
Lora: Remove duplicate LinkCheckReq MAC command

When application requests link check request with add_link_check_request()
it was added to MAC command buffer. Again when actual TX was started,
stack cherry-picked the request into MAC buffer again resulting in a duplicate
entry in the buffer.

Functionality is changed now so that add_link_check_request() does not add
the request into MAC command buffer but it is cherry-picked into the buffer when
TX is issued.

kjbracey-arm/mbed,betzw/mbed-os,kjbracey-arm/mbed,c1728p9/mbed-os,andcor02/mbed-os,betzw/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,c1728p9/mbed-os,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,betzw/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,betzw/mbed-os,betzw/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,mbedmicro/mbed,betzw/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,andcor02/mbed-os