net/mlx5e: Fix use-after-free when reverting termination table

[ Upstream commit 52c795af04441d76f565c4634f893e5b553df2ae ]

When having multiple dests with termination tables and second one
or afterwards fails the driver reverts usage of term tables but
doesn't reset the assignment in attr->dests[num_vport_dests].termtbl
which case a use-after-free when releasing the rule.
Fix by resetting the assignment of termtbl to null.

Fixes: 10caabda ("net/mlx5e: Use termination table for VLAN push actions")
Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>