pimd: Restarting Quagga sometimes lost mroutes

pimd: Restarting Quagga sometimes lost mroutes

When on a intermediate switch between the FHR and RP
when Quagga is restarted. Pimd is coming up so fast
and getting the S,G join before networking is properly
working on the switch.  We would never install the
mroute in this case.

What was happening is that the scan of the S,G was
occurring and we were figuring out who we should talk
to but we were never installing the route for it.

Notice that we've never installed the route and install it
if the mroute has changed.

Ticket: CM-12460
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>