[cleanup] Remove unnecessary mcast tests (#92)

The exclusion/prune and no_admin_ula mcast integration tests were
unnecessary  and part of previously configurable code that was made
obsolete during the last review cycle of the large mcast PR.

The exclusion/prune test was being flaky on CI, but didn't set up proper
MAC linking anyway. It's not useful because we force 0 for the exclusion
flag when we configure replication on the underlay groups.

Includes:
  * use oxnet's derive mac facility for tests, updating the dep
  * mcast integration test comment cleanup
  * move P4 # comment to //

Author: zeeshanlakhani

Cargo.lock

@@ -44,7 +44,7 @@ omicron-common = { git = "https://github.com/oxidecomputer/omicron", branch= "ma
 oximeter = { git = "https://github.com/oxidecomputer/omicron", branch = "main" }
 oximeter-producer = { git = "https://github.com/oxidecomputer/omicron", branch = "main" }
 oximeter-instruments = { git = "https://github.com/oxidecomputer/omicron", branch = "main", default-features = false, features = ["kstat"] }
-oxnet = { version = "0.1.2", default-features = false, features = ["schemars", "serde"] }
+oxnet = { version = "0.1.3", default-features = false, features = ["schemars", "serde"] }
 propolis = { git = "https://github.com/oxidecomputer/propolis" }
 sled-agent-client = { git = "https://github.com/oxidecomputer/omicron", branch = "main" }
 smf = { git = "https://github.com/illumos/smf-rs" }