net/mlx5: convert to new udp_tunnel infrastructure

Allocate nic_info dynamically - n_entries is not constant.

Attach the tunnel offload info only to the uplink representor.
We expect the "main" netdev to be unregistered in switchdev
mode, and there to be only one uplink representor.

Drop the udp_tunnel_drop_rx_info() call, it was not there until
commit b3c2ed21 ("net/mlx5e: Fix VXLAN configuration restore after function reload")
so the device doesn't need it, and core should handle reloads and
reset just fine.

v2:
 - don't drop the ndos on reprs, and register info on uplink repr.
v4:
 - Move netdev tunnel structure handling to en_main.c

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>