net: phy: simplify phy_link_change arguments

This function was introduced to allow for different handling of
link up and link down events particularly with regard to the
netif_carrier. The third argument do_carrier allowed the flag to
be left unchanged.

Since then the phylink has introduced an implementation that
completely ignores the third parameter since it never wants to
change the flag and the phylib always sets the third parameter
to true so the flag is always changed.

Therefore the third argument (i.e. do_carrier) is no longer
necessary and can be removed. This also means that the phylib
phy_link_down() function no longer needs its second argument.

Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>