pre-boot plugged SFP autoneg advertisement

[<markus.stockhausen@gmx.de>]

Hi,

I'm currently analyzing an issue where a pre-boot-plugged SFP module 
comes up with autoneg=no advertisement during boot. After an
unplug/replug autoneg=yes advertisement is chosen. 

The following addition in phylink_start() just before the call to
phylink_mac_initial_config() mitigiates this.

+  /* If an SFP module was already present before phylink_start() was
+   * called, phylink_sfp_set_config() was unable to call
+   * phylink_mac_initial_config() as phylink was not yet started.
+   * Ensure the SFP capabilities are reflected in advertising.
+   */
+  if (pl->sfp_bus && !linkmode_empty(pl->sfp_support))
+    linkmode_copy(pl->link_config.advertising, pl->sfp_support);

Remark! This is about the OpenWrt Realtek Switch ecosystem with 
kernel 6.18 where we are working hard to get hardware up and 
running. We still rely heavily on pcs/dsa downstream drivers. So 
I'm unsure if my observation/idea regarding upstream phylink is 
right.

Thanks for your feedback in advance.

Markus