Deprecate egress_port (uint32) in favor of egress (bytes) in Replica

[antoninbas]

This is to ensure consistency with the watch_port field. See https://github.com/p4lang/p4runtime/pull/317

Fixes #329

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[smolkaj]

Bump. We are starting to use multicast. Would be great to get this submitted.

[antoninbas]

Bump. We are starting to use multicast. Would be great to get this submitted.

I don't mind merging this as it is. I know that other parts of the spec also needs to be tackled: the Index message, used to address Counter and Meter entries, should also support translation and its type should be changed to bytes (indexing a counter using a port value is a pretty common scenario). However, that can be done in a future PR.

[antoninbas]

@smolkaj I rebased the PR, could you take a look?