net/mlx5e: Fix wrong use of skb_tcp_all_headers() with encapsulation

Use skb_inner_tcp_all_headers() instead of skb_tcp_all_headers() when
transmitting an encapsulated packet in mlx5e_tx_get_gso_ihs().

Fixes: 504148fe ("net: add skb_[inner_]tcp_all_headers helpers")
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>