in_node_exporter_metrics: netstat collector missing TcpExt_*/IpExt_* from /proc/net/netstat

[yurkovoznyak]

Is your feature request related to a problem? Please describe.
The node_exporter_metrics plugin's netstat collector documents itself as "Exposes network statistics from /proc/net/netstat" (https://docs.fluentbit.io/manual/data-pipeline/inputs/node-exporter-metrics).

In practice, the collector reads /proc/net/snmp (not /proc/net/netstat) and only processes the Tcp: and Udp: sections. None of the TcpExt: / IpExt: counters from /proc/net/netstat are emitted

Describe the solution you'd like
Extend the existing netstat collector to also read /proc/net/netstat (in addition to /proc/net/snmp) and emit node_netstat_TcpExt_* / node_netstat_IpExt_* from its TcpExt: / IpExt: sections.

Additional context

• Fluent-bit version where the gap was observed: 5.0.3 (fluent/fluent-bit:5.0.3)
• Doc page that references /proc/net/netstat as the source: https://docs.fluentbit.io/manual/data-pipeline/inputs/node-exporter-metrics