Allows to get the unique frame identifier for the given frame.
Inside Vortex Library, every frame created is flagged with an unique frame identifier which is not part of the BEEP protocol, transmitted or received from the remote side.
This unique identifiers was created for the internal Vortex Library support but, it has become a useful mechanism to have frames identified.
Application level could use this value to implement fast frame recognition rather than using vortex_frame_are_equal, which is more expensive.
Vortex Library will ensure, as long as the process is in memory that every unique identifier returned/generated for a frame will be unique.