auditbeat,filebeat,packetbeat: mac addresses are not formatted according to ECS

[efd6]

In a number of places in {auditbeat,filebeat,packetbeat}, the stdlib net.HardwareAddr String method is used to format MAC addresses. The format used by the standard library uses lowercase octets separated by colons rather than uppercase separated by dashes as specified in the ECS. There is also an instance of this in libbeat, but this is addressed by #32264/#32265.

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[efd6]

I think this is now done.