bgpd: Fix router-id update handling for route-leaking

bgpd: Fix router-id update handling for route-leaking

If the default BGP instance is importing routes from another instance and
the latter has a router-id update, the update handler needs to handle the
default instance in a special way.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Chirag Shah <chirag@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-26007
Reviewed By: CCR-9108
Testing Done: Detailed verification in 3.x