net: stmmac: move initialisation of priv->tx_lpi_timer to stmmac_open()

net: stmmac: move initialisation of priv->tx_lpi_timer to stmmac_open()

The initialisation of priv->tx_lpi_timer only happens once during the
lifetime of the driver, which is during the initial administrative
open of the device. Move this initialisation out of __stmmac_open()
into stmmac_open().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1v119y-0000000774A-2vvl@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>