BR: improve metrics

[kormat]

• Revocations forked by receiving interface metric
• SCMP echos/traceroutes/recordpaths
• Basically anything that can cause the router to drop a packet, to return an scmp error, or to log an error. E.g.:
  • Parse errors
  • Validation errors
  • Processing errors
  • Routing errors
• Ctrl plane metrics. E.g.:
  • Dispatcher errors/reconnections - depends on either lib/sock/reliable: expose metrics #3183 or lib/sock/reliable/reconnect: expose events to application #3185
  • Packets in/out
  • Parse errors
  • Unsupported payloads
  • ifstateinfo payloads received
  • ifstatereq payloads sent
  • revinfo parse errors

[scrye]

Renamed similarly to other issues.

[sgmonroy]

• SCMP echos - From the BR point of view, they are just like any other packet. Only traceroute and recordpath are HBH. SCMP echo metric should be kept by the dispatcher.
• Ctrl plane metrics. E.g.:
  • Dispatcher errors/reconnections - AFAIK there is no way to see the reconnections when they happen from the BR/app.