[inetstack] Do not print duplicate packet warning when receiving bare acks

[iyzhang]

Description

We often receive bare acks, especially from a Demikernel remote. These bare acks never bump the sequence number because they are not carrying data. However, we always print a warning saying that we received a duplicate packet.

How to Reproduce

Steps to reproduce the behavior:

1. Run this push simulation trace.
2. On the last received packet, which is a bare ack, a warning is printed that we've received a duplicate packet.

Expected Behavior

Bare acks are expected so we should not print anything.