systemc: gem5_to_tlm bridge should reuse existed tlm payload

Given a data path initiated from SystemC, routed by gem5, and handled
by SystemC finally.

SystemC -> gem5 -> SystemC

The target SystemC needs to get the original transaction object.
Otherwise, it would lose the extensions in the payload.

To fix the issue, we moves the SenderState class to public for reachibility.
After that, we refactor the logic converting between payload and packet
to make sure they can use the correct instance. Finally, we fix the
potential address change during routing.

Change-Id: Ic6d24e98454f564f7dd6b43ad8c011e1ea7ea433
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63771
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
4 files changed