ospfd, ospf6d: perform GR consistency check only when necessary

ospfd, ospf6d: perform GR consistency check only when necessary

The GR code should check for topology changes only upon the receipt
of Router-LSAs and Network-LSAs. Other LSAs types don't affect the
topology as far as a restarting router is concerned.

This optimization reduces unnecessary computations when the
restarting router receives thousands of inter-area LSAs or external
LSAs while coming back up.

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