ospf6d: spf calculation w/ multiple router lsas

ospf6d: spf calculation w/ multiple router lsas

An OSPFv3 enabled Router can originate or receive
multiple Link State-IDs for Router LSAs.
As per RFC 5340 A 4.3, more than one Router LSAs,
from given Vertex is considered (as concatenated)
single large Router LSA.

Created hidden show command to simulate concatenated
large LSA from advertising/self Router LSAs.

Ticket:CM-19329
Reviewed By:
Testing Done:
Simulate 160 subinterfaces between R1 === R2--R3,
This triggers R1 and R2 to generate multiple link state
IDs for Router LSAs. During SPF calculation only aggregated
single router LSA processed and SPF tree formed.

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>