Network test needs to focus on advertized speeds, not supported speeds

[Jeff Lane ]

As we've learned, chipsets can be rate limitied and while a chipset may support one speed, it's max advertized may be lower. For example:
Settings for enP8p1s0:
 Supported ports: [ FIBRE ]
 Supported link modes: 1000baseKX/Full
                         10000baseKX4/Full
                         10000baseKR/Full
                         40000baseCR4/Full
                         40000baseSR4/Full
                         56000baseCR4/Full
                         56000baseSR4/Full
 Supported pause frame use: Symmetric Receive-only
 Supports auto-negotiation: Yes
 Supported FEC modes: Not reported
 Advertised link modes: 1000baseKX/Full
                         10000baseKX4/Full
                         10000baseKR/Full
                         40000baseCR4/Full
                         40000baseSR4/Full
 Advertised pause frame use: Symmetric
 Advertised auto-negotiation: Yes
 Advertised FEC modes: Not reported
 Speed: 40000Mb/s
 Duplex: Full
 Port: Direct Attach Copper
 PHYAD: 0
 Transceiver: internal
 Auto-negotiation: off
 Supports Wake-on: d
 Wake-on: d
 Current message level: 0x00000014 (20)
          link ifdown
 Link detected: yes

Currently the Network script will fail if the detected network speed is lower than the max. The intention was to verify network speed against the advertised max, but it seems to be checking against the supported max instead. For example, this controller failed:

ERROR:root:Detected link speed (40000) is lower than detected max speed (56000)
ERROR:root:Check your device configuration and try again.
ERROR:root:If you want to override and test despite this under-speed link, use
ERROR:root:the --underspeed-ok option.

It advertises 40Gb max, and is connected on a 40Gb link, yet failed because the chipset supported max says 56Gb.

SO, we need to fix this to do two things:

1: It needs to compare the link speed to the advertized max speed, NOT the supported max speed.
2: We need to know when advertised and supported are different, so it should drop a warning if the advertised max is different than the supported max (higher OR lower).

[Maksim Beliaev (beliaev-maksim)]

Bug was migrated to GitHub: https://github.com/canonical/checkbox/issues/108.
Bug is no more monitored here.