MINOR: quic: Prepare quic_frame struct duplication

MINOR: quic: Prepare quic_frame struct duplication

We want to track the frames which have been duplicated during retransmissions so
that to avoid uselessly retransmitting frames which would already have been
acknowledged. ->origin new member is there to store the frame from which a copy
was done, ->reflist is a list to store the frames which are copies.
Also ensure all the frames are zeroed and that their ->reflist list member is
initialized.
Add QUIC_FL_TX_FRAME_ACKED flag definition to mark a TX frame as acknowledged.