net: sfp: provide sfp_get_module_caps()

Provide a function to retrieve the current sfp_module_caps structure
so that upstreams can get the entire module support in one go.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1uydVj-000000061WQ-3q47@rmk-PC.armlinux.org.uk


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