net: pcs: xpcs: correct pause resolution

xpcs was indicating symmetric pause should be enabled regardless of
the advertisements by either party. Fix this to use
linkmode_resolve_pause() now that we're no longer obliterating the
link partner's advertisement by logically anding it with our own.

This is transitional, the function will be entirely replaced with
phylink_resolve_c73() in the following patch.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>