Quagga: Static LSP configuration

Quagga: Static LSP configuration

Add support for statically configuring MPLS transit LSPs. This allows the
configuration of ILM to one or more NHLFE, as defined in RFC 3031. The
currently supported nexthop types are IPv4 or IPv6.

The two label operations supported are swap and PHP; the latter is configured
by specifying the out-label as "implicit-null". Note that the operation is
against the label, so it should be the same for all NHLFEs.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-4804, ...
Reviewed By: CCR-3085
Testing Done: In combination with other patches