ice: add NULL check in eswitch lag check

[ Upstream commit 3ce58b01 ]

The function ice_lag_is_switchdev_running() is being called from outside of
the LAG event handler code.  This results in the lag->upper_netdev being
NULL sometimes.  To avoid a NULL-pointer dereference, there needs to be a
check before it is dereferenced.

Fixes: 776fe199 ("ice: block default rule setting on LAG interface")
Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>