realtek: dsa: enhance pcs_get_state() for RTL83xx

realtek: dsa: enhance pcs_get_state() for RTL83xx

Currently the SerDes driven SFP ports give strange ethtool readings
on RTL83xx devices. Especially duplex and speed are shown even if
no link is up and running. That leads to confusion because the MAC
reports arbitrary values.

Enhance the readout by refactoring the pcs_get_state() function.
Calculate speed/duplex/pause only if link is detected. Additionally
add reporting of 10G for SFP+ on RTL839x.

ethtool for empty SFP cage before/after

root@OpenWrt:~# ethtool lan9
Settings for lan9:
        Supported ports: [ MII ]
        Supported link modes:   1000baseT/Full
                                1000baseKX/Full
                                1000baseX/Full
                                1000baseT1/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  1000baseT/Full
                                1000baseKX/Full
                                1000baseX/Full
                                1000baseT1/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 10Mb/s
        Duplex: Half
        Port: MII
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Link detected: no

root@OpenWrt:~# ethtool lan9
Settings for lan9:
        Supported ports: [ MII ]
        Supported link modes:   1000baseT/Full
                                1000baseKX/Full
                                1000baseX/Full
                                1000baseT1/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  1000baseT/Full
                                1000baseKX/Full
                                1000baseX/Full
                                1000baseT1/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: Unknown!
        Duplex: Unknown! (255)
        Port: MII
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Link detected: no

ethtool with inserted but NOT connected 1G module before/after

root@OpenWrt:~# ethtool lan9
Settings for lan9:
        Supported ports: [ FIBRE ]
        Supported link modes:   1000baseX/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  1000baseX/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: FIBRE
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Link detected: no

root@OpenWrt:~# ethtool lan9
Settings for lan9:
        Supported ports: [ FIBRE ]
        Supported link modes:   1000baseX/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  1000baseX/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: Unknown!
        Duplex: Unknown! (255)
        Port: FIBRE
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Link detected: no

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/19524
Signed-off-by: Robert Marko <robimarko@gmail.com>