Enhanced support to handle S flag, D flag and A flags in IS-IS

You can set the S flag to allow the label binding type, length and values (TLV) to leak through the IS-IS level (Level 1 or Level 2). You can set the A flag to program the penultimate-hop popping (PHP). You can set the D flag to prevent the leaking of the label binding TLV from Level 2 back to Level 1. Use the no-binding configuration statement at the [edit protocols isis source-packet-routing no-binding-sid-leaking] hierarchy level to disable label binding TLV leaks.