net: pcs: xpcs: correct lp_advertising contents

lp_advertising is supposed to reflect the link partner's advertisement
unmodified by the local advertisement, but xpcs bitwise ands it with
the local advertisement prior to calculating the resolution of the
negotiation.

Fix this by moving the bitwise and to xpcs_resolve_lpa_c73() so it can
place the results in a temporary bitmap before passing that to
ixpcs_get_max_usxgmii_speed().

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>