NETIF_F_RX_UDP_TUNNEL_PORT is special, in that we need to do more than
just flip the bit in dev->features. When disabling we must also clear
currently offloaded ports from the device, and when enabling we must
tell the device to offload the ports it can.

Because vxlan stores its sockets in a hashtable and they are inserted at
the head of per-bucket lists, switching the feature off and then on can
result in a different set of ports being offloaded (depending on the
HW's limits).
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>