ixgbe: configure UDP tunnel port

Add UDP tunnel port add/del support on ixgbe. Now only
support VxLAN port configuration.
Although according to the specification the VxLAN port has
a default value 4789, it can be changed. We support VxLAN
port configuration to meet the change.
Note, the default value of VxLAN port in ixgbe NICs is 0. So
please set it when using VxLAN off-load.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>