net: stmmac: restart LPI timer after cleaning transmit descriptors

Fix a bug in the LPI handling, where it is possible to immediately
enter LPI mode after cleaning the transmit descriptors when all queues
are empty rather than waiting for the LPI timeout to expire.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tXItg-000MBg-TW@rmk-PC.armlinux.org.uk


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