This commit implements a new option in the cbf-emulator to send heaps
out of order, which in turn can be used to test how the receiver reacts
to different situations. The option specifies how many data heaps to
send *before* the start-of-stream heap, with a default value of 0 (send
heaps in order), and negative values meaning that the start-of-stream
heap should never be sent.

In order to support delaying for the maximum amount of data heaps, we
now need to potentially send the SOS heap at stop() time.

This work is part of YAN-1142

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Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>