rina-normal: rtx: use rtx_tmr_next to manage rtxq removal and retransmission
rina-normal: rtx: use rtx_tmr_next to manage rtxq removal and retransmission

The algorithm has been modified so that retransmitted PDUs are not put
anymore at the tail of the rtxq, preserving the seqnum sorting.

The rtx_tmr_next pointer de-facto represents a shifted version of
the rtx list.

vmaffione/rlite,vmaffione/rlite,vmaffione/rlite,autrimpo/rlite,autrimpo/rlite,autrimpo/rlite,vmaffione/rlite,autrimpo/rlite