isisd: give precedence to new-style TLVs when generating routes

isisd: give precedence to new-style TLVs when generating routes

When both old and new-style TLVs exist for a particular prefix, give
precedence to the new-style TLV (like JUNOS does) when generating
routes from the SPT. This changes the current behavior which is to
generate a route for both TLVs, whereas the first is overwritten by
the second in a non-deterministic order (i.e. either the old-style
or the new-style TLV can "win" depending on how the SPF TENTative
list is arranged).

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>