be2net: VxLAN offload should be re-enabled when only 1 UDP port is left

We disable VxLAN offload when more than 1 UDP port is added to the driver,
since Skyhawk doesn't support offload with multiple ports. The existing
driver design expects the user to delete all port configurations and create
a configuration with a single UDP port for VxLAN offload to be re-enabled.
Remove this restriction by tracking the ports added and re-enabling offload
when ports get deleted and only 1 port is left.

Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Reviewed-by: Sathya Perla <sathya.perla@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>