ot::Spinel::Buffer::InFrameGetLastTag() const method

Returns the tag assigned to last successfully written/added frame to NcpBuffer (i.e., last input frame for which `InFrameEnd()` was called and returned success status). The tag is a unique value (within currently queued frames) associated with a frame in the `Buffer`. The tag can be used to identify the same frame when it is read and removed from the NcpBuffer. Tags can be compared using operator `==`.