[f-nsp] Explicit Null MPLS label support on MLX

[David Ball]

  I don't currently have an MLX so I can't check on the router, but I
can't find any mention in the 3.8.0.0 config guide as to whether
explicit null can be configured for MPLS.  I only see mention to the
fact that label 3 is advertised to the penultimate LSR for the purpose
of performing penultimate hop popping.  Any idea if explicit null can
be sent, to ensure the packet stays MPLS-encapsulated until it reaches
the ultimate LER ?

David