When a function is "inlined" it means that the code to be executed inside the function is promoted into the calling function, thereby avoiding the overhead of saving registers, jumping into the function, and restoring the registers afterwards (search online for "ABI" for details on this).
It's not possible to inline a kernel call, it makes no sense because the processor executing the kernel code (the GPU) is not the same as the processor launching the kernel (the CPU).
Even with dynamic parallelism it makes no sense since the semantics mean that the child kernel can be run anywhere, not necessarily on the same SM.