mem: Check response only when needed in CommMonitor

mem: Check response only when needed in CommMonitor

CommMonitor checks pkt->isResponse() for all packets in recvAtomic().
This assertion fails when packets don't need response, such as WritebackDirty.
This change fixes this.

Signed-off-by: Chun-Chen TK Hsu
Change-Id: I168e349e179b14fa5472698d9300478dc89693fb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19428
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>