mem-garnet: Use static allocation in NetworkInterface

mem-garnet: Use static allocation in NetworkInterface

Use static allocation for the pointers managed by NetworkInterface.

Change-Id: Ib97d95165337659f92cb8a078020692baae5b5ca
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24247
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Srikant Bharadwaj <srikant.bharadwaj@amd.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>