net: stmmac: avoid PHY speed change when configuring MTU

net: stmmac: avoid PHY speed change when configuring MTU

There is no need to do the speed-down, speed-up dance when changing
the MTU as there is little power saving that can be gained from such
a brief interval between these, and the autonegotiation they cause
takes much longer.

Move the calls to phylink_speed_up() and phylink_speed_down() into
stmmac_open() and stmmac_release() respectively, reducing the work
done in the __-variants of these functions.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1v945T-0000000AmeV-2BvU@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>