net/mlx5e: Re-order route and encap header memory allocation

Change the order to first route IPv4/6 and return if error. Only after
successful route continue to allocate an encap header, with no
functional change.

Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>