net: phylink: simplify how SFP PHYs are attached

There are a few issues with how SFP PHYs are attached:

a) The phylink_sfp_connect_phy() and phylink_sfp_config_phy() code
   validates the configuration three times:

1. To discover the support/advertising masks that the PHY/PCS/MAC
   can support in order to select an interface.
2. To validate the selected interface.
3. When the PHY is brought up after being attached, another validation
   is done.

   This is needlessly complex.

b) The configuration is set prior to the PHY being attached, which
   means we don't have the PHY available in phylink_major_config()
   for phylink_pcs_neg_mode() to make decisions upon.

We have already added an extra step to validate the selected interface,
so we can now move the attachment and bringup of the PHY earlier,
inside phylink_sfp_config_phy(). This results in the validation at
step 2 above becoming entirely unnecessary, so remove that too.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1t3bcb-000c8H-3e@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>