net/mlx5e: Make sure the FW max encap size is enough for ipv4 tunnels

Otherwise the code that fills the ipv4 encapsulation headers could be writing
beyond the allocated headers buffer.

Fixes: a54e20b4

 ('net/mlx5e: Add basic TC tunnel set action for SRIOV offloads')
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>