srv6: add per-nexthop encap source address

[rjarry]

FRR 10.8 added a per-nexthop encapsulation source address to nexthop_add_srv6_seg6(). This series adds per-nexthop encap_src support to grout's SRv6 output nexthops and plumbs it through the FRR dplane plugin.

When an SRv6 output nexthop has an explicit encap_src set, the datapath uses it directly as the outer IPv6 source instead of the global tunnel source or the interface preferred address. An internal flags field avoids a 16-byte comparison in the hot path.

The series also updates FRR build support: bumps 10.5 to 10.5.4, adds 10.7 (rc1), and changes the default build version to 10.6.

Summary

• Add per-nexthop SRv6 encap-src support end-to-end (CLI → control plane API structs → FRR dplane plugin → datapath encapsulation).
• Propagate an explicit encap_src as the outer IPv6 header source; when encap_src is unspecified, fall back to the configured tunnel source / interface preferred address.
• Extend SRv6 nexthop output state with an encap_src field plus SR_ENCAP_F_SRC presence flag, and in srv6_output_process() use the flagged encap_src directly to avoid doing a 16-byte IPv6 comparison in the datapath hot path.
• Update SRv6 nexthop equality/import/export logic to include encap_src, setting SR_ENCAP_F_SRC only when it’s not the unspecified IPv6 address.
• Add rte_ipv6_addr_is_unspec() helper in api/gr_net_compat.h to detect unspecified IPv6 addresses by checking all 16 bytes.
• Update CLI parsing and display for SRv6 nexthops/seglists to accept an optional SRC parameter and to show ENCAP_SRC only when encap_src is not unspecified.
• Extend FRR dplane SRv6 SR output nexthop handling to propagate encap_src to nexthop_add_srv6_seg6() for FRR >= 10.8.0, and populate the plugin-side encap_src from the FRR seglist source when building GR_NH_T_SR6_OUTPUT.
• Bump API handshake version GR_API_VERSION from 3 to 4.
• Add smoke tests validating per-nexthop encap-source behavior: smoke/srv6_test.sh and smoke/srv6_encapsrc_frr_test.sh (skips when installed FRR < 10.8.0).
• Update FRR build/compat support: default frr_version to 10.6, add 10.7 (rc1) support, bump 10.5 wrap to 10.5.4, and adjust CI build matrix to use 10.7 for the gcc-14 aarch64 configuration.

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⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between c903ada and fda8215.

📒 Files selected for processing (11)

• api/gr_api.h
• api/gr_net_compat.h
• frr/rt_grout.c
• modules/srv6/api/gr_srv6.h
• modules/srv6/cli/route.c
• modules/srv6/control/route.c
• modules/srv6/control/srv6.h
• modules/srv6/datapath/srv6_output.c
• smoke/_init_frr.sh
• smoke/srv6_encapsrc_frr_test.sh
• smoke/srv6_test.sh

📝 Walkthrough

Walkthrough

Adds optional per-nexthop SRv6 encapsulation source handling across public and private nexthop data, CLI parsing and display, control-plane conversion, datapath header construction, and FRR route installation. Updates FRR version options, packages, and CI coverage. Adds smoke tests that configure explicit encapsulation sources and verify captured outer IPv6 source addresses.

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