net/mlx5e: Fix check if netdev is bond slave

Bond events handler uses bond_slave_get_rtnl to check if net device
is bond slave. bond_slave_get_rtnl return the rcu rx_handler pointer
from the netdev which exists for bond slaves but also exists for
devices that are attached to linux bridge so using it as indication
for bond slave is wrong.

Fix by using netif_is_lag_port instead.

Fixes: 7e51891a ("net/mlx5e: Use netdev events to set/del egress acl forward-to-vport rule")
Signed-off-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Raed Salem <raeds@nvidia.com>
Reviewed-by: Ariel Levkovich <lariel@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>