be2net: convert to new udp_tunnel_nic infra

Convert be2net to new udp_tunnel_nic infra. NIC only takes one VxLAN
port. Remove the port tracking using a list. The warning in
be_work_del_vxlan_port() looked suspicious - like the driver expected
ports to be removed in order of addition.

be2net unregisters ports when going down and re-registers them (for
skyhawk) when coming up, but it never checks if the device is up
in the add_port / del_port callbacks. Make it use
UDP_TUNNEL_NIC_INFO_OPEN_ONLY. Sadly this driver calls its own
open/close functions directly so the udp_tunnel_nic_reset_ntf()
workaround is needed.

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