net: fman_memac: remove the now unnecessary checking for fixed-link

Since default_an_inband can be overriden by a fixed-link specification,
there is no need for memac to be checking for this before setting
default_an_inband. Remove this code and update the comment.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/E1sCJN1-00Ecr7-02@rmk-PC.armlinux.org.uk


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