Add processor that does service port to name translation

[danielnelson]

Feature Request

Proposal:

Add a new processor that can convert a tag containing a well-known port number to the registered service name, according to the net.LookupPort function or similar.

Current behavior:

N/A

Desired behavior:

[[processors.lookup_port]]
  tag = "port"

  ## If set, write port to new tag key
  # dest = "service"

- foo,port=443 bar=42
+ foo,port=443,service=https bar=42

Use case:

Enrich the output of the sflow input.