Add advanced udp metrics

[Andrewmatilde]

Add Advanced UDP Statistics

What

Add advanced UDP statistics for problem diagnosis, sourcing data from /proc/net/snmp. Currently, cAdvisor only retrieves basic UDP metrics from /proc/net/udp and /proc/net/udp6, which tend to be unreliable due to frequent value changes.
related: #3657

Why

• Current UDP metrics are of low quality due to frequent value changes leading to inconsistent data
• /proc/net/snmp provides more comprehensive UDP statistics, similar to existing advanced TCP metrics

How

1. Add new UdpAdvancedStat structure with the following fields:

• InDatagrams - Total number of datagrams successfully received
• NoPorts - Number of datagrams discarded due to no available ports
• InErrors - Number of datagrams discarded due to errors
• OutDatagrams - Total number of datagrams successfully transmitted
• RcvbufErrors - Number of datagrams dropped due to insufficient receive buffer
• SndbufErrors - Number of datagrams dropped due to insufficient send buffer
• InCsumErrors - Number of datagrams discarded due to checksum errors
• IgnoredMulti - Number of datagrams discarded due to ignored multicast

2. Parse these metrics from /proc/net/snmp and add them to container statistics

Example output:

"udp_advanced": {
    "InDatagrams": 174527561,
    "NoPorts": 8979,
    "InErrors": 8,
    "OutDatagrams": 174548568,
    "RcvbufErrors": 8,
    "SndbufErrors": 0,
    "InCsumErrors": 0,
    "IgnoredMulti": 0
}

Testing

• Added unit tests to verify UDP statistics parsing from /proc/net/snmp
• Manually tested metric collection