bgpd: Handle multiple simultaneous changes for a VNI correctly

bgpd: Handle multiple simultaneous changes for a VNI correctly

Ensure that if multiple parameters for a VNI change simultaneously, the
changes are processed correctly. The changes of interest are the local
tunnel IP address and the tenant VRF to which this VNI is attached. The
former is used to originate type-3 routes as well as set the next hop of
all routes, the latter helps to determine the route targets and VNIs to
include in the route.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Mitesh Kanjariya <mitesh@cumulusnetworks.com>
Ticket: CM-19099
Reviewed By: CCR-7102
Testing Done:
1. Manually reproduced problem and verified fix.
2. Additional trigger events tested with fix.