bgpd: add meta queue in bgp

This commit introduces meta queue to the BGP process_queue which is
helpful in having a priority of lists where some routes can be processed
earlier than 'other' routes. This is similar to how meta queue is
present in zebra.

After Fix:
---------

For testing, note that all 100.x routes are marked as Early routes which
got enqueued and dequeued first before Other routes in every batch of
updates. Also, the items are dequeued in FIFO order.

switch# cat /var/log/frr/bgpd.log | grep sub-queue
2024/12/06 19:19:42.788014 BGP: [V64FH-G6883] 88.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:42.856127 BGP: [V64FH-G6883] 100.90.9.186/32 queued into sub-queue Early Route
2024/12/06 19:19:42.856138 BGP: [V64FH-G6883] 100.90.9.187/32 queued into sub-queue Early Route
2024/12/06 19:19:42.886715 BGP: [V64FH-G6883] 66.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.022835 BGP: [V64FH-G6883] 33.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.058842 BGP: [V64FH-G6883] 44.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.092365 BGP: [V64FH-G6883] 55.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.540770 BGP: [ZAPXS-9754G] 100.90.9.186/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.541233 BGP: [ZAPXS-9754G] 100.90.9.187/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.541523 BGP: [ZAPXS-9754G] 88.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:43.602094 BGP: [V64FH-G6883] 88.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.649083 BGP: [V64FH-G6883] 100.90.9.186/32 queued into sub-queue Early Route
2024/12/06 19:19:43.649092 BGP: [V64FH-G6883] 100.90.9.187/32 queued into sub-queue Early Route
2024/12/06 19:19:43.649148 BGP: [V64FH-G6883] 77.0.0.9/32 queued into sub-queue Other Route
2024/12/06 19:19:43.712282 BGP: [V64FH-G6883] 100.90.9.138/32 queued into sub-queue Early Route
2024/12/06 19:19:43.712314 BGP: [V64FH-G6883] 100.90.9.139/32 queued into sub-queue Early Route
2024/12/06 19:19:43.817194 BGP: [V64FH-G6883] 100.90.8.58/32 queued into sub-queue Early Route
2024/12/06 19:19:43.817205 BGP: [V64FH-G6883] 100.90.8.59/32 queued into sub-queue Early Route
2024/12/06 19:19:43.942464 BGP: [ZAPXS-9754G] 100.90.9.186/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.942530 BGP: [ZAPXS-9754G] 100.90.9.187/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.942550 BGP: [ZAPXS-9754G] 100.90.9.138/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.942738 BGP: [ZAPXS-9754G] 100.90.9.139/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.942763 BGP: [ZAPXS-9754G] 100.90.8.58/32 dequeued from sub-queue Early Route
2024/12/06 19:19:43.942788 BGP: [ZAPXS-9754G] 100.90.8.59/32 dequeued from sub-queue Early Route
2024/12/06 19:19:44.558611 BGP: [ZAPXS-9754G] 66.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:44.893541 BGP: [ZAPXS-9754G] 33.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:45.171794 BGP: [ZAPXS-9754G] 44.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:45.453137 BGP: [ZAPXS-9754G] 55.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:45.685269 BGP: [ZAPXS-9754G] 88.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 19:19:45.764752 BGP: [ZAPXS-9754G] 77.0.0.9/32 dequeued from sub-queue Other Route

With 'update-delay' feature (EOIU marker):
------------------------------------------

switch# vtysh -c "show run bgp" | grep update-delay
 update-delay 40

switch# cat /var/log/frr/bgpd.log | grep sub-queue
2024/12/06 23:27:46.124461 BGP: [V64FH-G6883] 22.0.0.9/32 queued into sub-queue Other Route
2024/12/06 23:27:46.160224 BGP: [V64FH-G6883] 100.90.8.11/32 queued into sub-queue Early Route
2024/12/06 23:27:46.219663 BGP: [W9QTR-P4REP] EOIU Marker queued into sub-queue EOIU Marker
2024/12/06 23:27:46.269711 BGP: [ZAPXS-9754G] 100.90.8.11/32 dequeued from sub-queue Early Route
2024/12/06 23:27:46.270980 BGP: [ZAPXS-9754G] 22.0.0.9/32 dequeued from sub-queue Other Route
2024/12/06 23:27:46.404868 BGP: [RBX2V-K33CZ] EOIU Marker dequeued from sub-queue EOIU Markera

Ticket: #4200787
Signed-off-by: Karthikeya Venkat Muppalla <kmuppalla@nvidia.com>
Signed-off-by: Donald Sharp <sharpd@nvidia.com>