[tcp/udp] Add a configuration option for network type

[taylor-swanson]

Overview

Go provides an argument to the Listen function (likewise for ListenTCP and ListenUDP) to specify the type of network (IPv4, IPv6, or both/auto) to be used when creating the listener. The network type for the TCP and UDP inputs are tcp and udp, respectively, and there is currently no way to override this value. Certain situations may require locking down the type of network being used (such as providing a hostname or using localhost).

The TCP input would accept these values for the network type:

• tcp (default)
• tcp4
• tcp6

The UDP input would accept these values for the network type:

• udp (default)
• udp4
• udp6

Examples

filebeat.inputs:
- type: tcp
  max_message_size: 10MiB
  host: "localhost:9000"
  network: tcp4

filebeat.inputs:
- type: udp
  max_message_size: 10KiB
  host: "localhost:8080"
  network: udp4

Acceptance Criteria

• When no option is provided, the default value (udp or tcp) is used
• When an option is provided, it must be a valid value, all other values must raise an error
• The option/default is applied to the listener and can be verified in netstat (or equivalent) output
• Documentation added for new config fields

[elasticmachine]

Pinging @elastic/sec-deployment-and-devices (Team:Security-Deployment and Devices)