Improve tunnel interface creation performance

Modify interface creation to allow creation of tunnel interfaces
without dedicated per tunnel output and tx nodes which are not
used for most tunnel types. Also changed interface-output node
function vnet_per_buffer_interface_output() so it does not rely
on hw_if_index as the next node index which is not flexible nor
efficient for large scale tunnel interfaces.

The improvenemts are done for VXLAN, VXLAN-GPE, GENEVE and GTPU
tunnels. GRE tunnel is still using per tunnel output nodes which
will be changed in a separate patch with other GRE enhencements.

Change-Id: I4123c01c0d2ead814417a867adb8c8a407e4df55
Signed-off-by: John Lo <loj@cisco.com>