The later device status check depends on E1000_STATUS_LU, which is
enabled by E1000_CTRL_SLU. Though E1000_STATUS_LU is not implemented
and E1000_STATUS_LU is always available in the current implementation,
be a bit nicer and set E1000_CTRL_SLU just in case the bit is
implemented in the future.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20221103025451.27446-1-akihiko.odaki@daynix.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>