P2MP - Fast MBB

This feature introduces fast make-before-break (fast MBB) for RSVP-TE P2MP LSPs. With fast MBB enabled, you achieve fast branch updates with the help of incremental additions to the original binary trees. By keeping the original binary trees intact, you can accomplish quick branch updates without incurring packet loss. As fast branch updates could lead to an unoptimized tree, the usual MBB, triggered by the kernel, follows fast MBB.