net/mlx5: Fix rtable reference leak

If the rt entry gateway family is not AF_INET for multipath device,
rtable reference is leaked.
Hence, fix it by releasing the reference.

Fixes: 5fb091e8 ("net/mlx5e: Use hint to resolve route when in HW multipath mode")
Fixes: e32ee6c7

 ("net/mlx5e: Support tunnel encap over tagged Ethernet")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>