dev: Make the EtherDevice class inherit EtherObject.

This avoids having to define two parallel versions of the getEthPort
function, and the complex dynamic_cast macrame in connectPorts().

Change-Id: I24c09864005ff39a049e50d7245ff17e9480edea
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17029
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2 files changed