bgpd: Fix announce SRv6 locally-generated routes to Zebra

[proelbtn]

Current bgpd can't announce SRv6 locally-generated routes to Zebra correctly because the MPLS label of locally-generated routes is not valid but sid_info->transposition_len is set to a non-zero value. This commit fixes such kinds of issues.

Before

pe1

pe1# show bgp vrf vrf20 ipv4 unicast 
BGP table version is 1, local router ID is 192.0.2.1, vrf id 4
Default local pref 100, local AS 65001
Status codes:  s suppressed, d damped, h history, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

    Network          Next Hop            Metric LocPrf Weight Path
 *> 172.16.0.0/24    0.0.0.0@2<               0         32768 ?

Displayed  1 routes and 1 total paths

pe1# show ip route vrf vrf20

pe1 - bgpd.log

2022/12/20 18:03:10 BGP: [X11WM-VBA5R] bgp_zebra_announce: p=172.16.0.0/24, bgp_is_valid_label: 0
2022/12/20 18:03:10 BGP: [V15FP-4CPVK] Tx route delete VRF 4 172.16.0.0/24 metric 0 tag 0 count 0 nhg 0
2022/12/20 18:03:10 BGP: [JMVGR-VQ1M1] bgp_zebra_announce: 172.16.0.0/24: announcing to zebra (recursion NOT set)

After

pe1

pe1# show bgp vrf vrf20 ipv4 unicast 
BGP table version is 1, local router ID is 192.0.2.1, vrf id 4
Default local pref 100, local AS 65001
Status codes:  s suppressed, d damped, h history, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

    Network          Next Hop            Metric LocPrf Weight Path
 *> 172.16.0.0/24    0.0.0.0@2<               0         32768 ?

Displayed  1 routes and 1 total paths

pe1# show ip route vrf vrf20
Codes: K - kernel route, C - connected, S - static, B - BGP,
       T - Table, v - VNC, V - VNC-Direct, D - SHARP,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

VRF vrf20:
B>* 172.16.0.0/24 [20/0] is directly connected, eth0 (vrf vrf10), weight 1, 00:00:42

pe1 - bgpd.log

2022/12/20 18:06:35 BGP: [X11WM-VBA5R] bgp_zebra_announce: p=172.16.0.0/24, bgp_is_valid_label: 0
2022/12/20 18:06:35 BGP: [V15FP-4CPVK] Tx route add VRF 4 172.16.0.0/24 metric 0 tag 0 count 1 nhg 0
2022/12/20 18:06:35 BGP: [JQXM8-V0CKB]   nhop [1]:  if 3 VRF 2 wt 0   
2022/12/20 18:06:35 BGP: [JMVGR-VQ1M1] bgp_zebra_announce: 172.16.0.0/24: announcing to zebra (recursion NOT set)

[ton31337]

[NetDEF-CI]

Continuous Integration Result: FAILED

Continuous Integration Result: FAILED

Test incomplete. See below for issues.
CI System Testrun URL: https://ci1.netdef.org/browse/FRR-PULLREQ2-8977/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

Get source / Pull Request: Successful

Building Stage: Incomplete

Ubuntu 16.04 arm8 build: Incomplete

(check logs for details)

Successful on other platforms/tests

• Ubuntu 18.04 i386 build
• Debian 11 amd64 build
• Ubuntu 16.04 i386 build
• Ubuntu 18.04 amd64 build
• Ubuntu 16.04 amd64 build
• Ubuntu 18.04 arm7 build
• CentOS 7 amd64 build
• Redhat 8 amd64 build
• OpenBSD 7 amd64 build
• FreeBSD 12 amd64 build
• Fedora 29 amd64 build
• Ubuntu 18.04 arm8 build
• Ubuntu 20.04 amd64 build
• Debian 9 amd64 build
• Redhat 9 amd64 build
• Ubuntu 18.04 ppc64le build
• Debian 10 amd64 build
• Ubuntu 22.04 amd64 build
• FreeBSD 11 amd64 build
• Ubuntu 16.04 arm7 build

### Basic Tests: Incomplete

[NetDEF-CI]

Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-PULLREQ2-8981/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

[ton31337]

LGTM