net/mlx5e: Fix del vxlan port command buffer memset

memset the command buffers rather than the pointers to them.

Fixes: b3f63c3d ("net/mlx5e: Add netdev support for VXLAN tunneling")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>