amd-xgbe: Avoid spurious link down messages during interface toggle

amd-xgbe: Avoid spurious link down messages during interface toggle

During interface toggle operations (ifdown/ifup), the driver currently
resets the local helper variable 'phy_link' to -1. This causes the link
state machine to incorrectly interpret the state as a link change event,
resulting in spurious "Link is down" messages being logged when the
interface is brought back up.

Preserve the phy_link state across interface toggles to avoid treating
the -1 sentinel value as a legitimate link state transition.

Fixes: 88131a812b16 ("amd-xgbe: Perform phy connect/disconnect at dev open/stop")
Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
Reviewed-by: Dawid Osuchowski <dawid.osuchowski@linux.intel.com>
Link: https://patch.msgid.link/20251010065142.1189310-1-Raju.Rangoju@amd.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>