net: stmmac: provide function for restarting sw LPI timer

Provide a function that encapsulates restarting the software LPI
timer when we have determined that the transmit path is busy, or
whether the EEE parameters have changed.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tXItW-000MBU-KQ@rmk-PC.armlinux.org.uk


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