ixgbe: convert to new udp_tunnel_nic infra

Make use of new common udp_tunnel_nic infra. ixgbe supports
IPv4 only, and only single VxLAN and Geneve ports (one each).

v2:
 - split out the RXCSUM feature handling to separate change;
 - declare structs separately;
 - use ti.type instead of assuming table 0 is VxLAN;
 - move setting netdev->udp_tunnel_nic_info to its own switch.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>