selftests: seg6: add selftest for NEXT-C-SID flavor in SRv6 End.X behavior

JIRA: https://issues.redhat.com/browse/RHEL-30814
Upstream Status: net.git commit 1c53717

commit 1c53717
Author: Paolo Lungaroni <paolo.lungaroni@uniroma2.it>
Date:   Sat Aug 12 20:09:26 2023 +0200

    selftests: seg6: add selftest for NEXT-C-SID flavor in SRv6 End.X behavior

    This selftest is designed for testing the support of NEXT-C-SID flavor
    for SRv6 End.X behavior. It instantiates a virtual network composed of
    several nodes: hosts and SRv6 routers. Each node is realized using a
    network namespace that is properly interconnected to others through veth
    pairs, according to the topology depicted in the selftest script file.
    The test considers SRv6 routers implementing IPv4/IPv6 L3 VPNs leveraged
    by hosts for communicating with each other. Such routers i) apply
    different SRv6 Policies to the traffic received from connected hosts,
    considering the IPv4 or IPv6 protocols; ii) use the NEXT-C-SID
    compression mechanism for encoding several SRv6 segments within a single
    128-bit SID address, referred to as a Compressed SID (C-SID) container.

    The NEXT-C-SID is provided as a "flavor" of the SRv6 End.X behavior,
    enabling it to properly process the C-SID containers. The correct
    execution of the enabled NEXT-C-SID SRv6 End.X behavior is verified
    through reachability tests carried out between hosts belonging to the
    same VPN.

    Signed-off-by: Paolo Lungaroni <paolo.lungaroni@uniroma2.it>
    Co-developed-by: Andrea Mayer <andrea.mayer@uniroma2.it>
    Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
    Reviewed-by: David Ahern <dsahern@kernel.org>
    Link: https://lore.kernel.org/r/20230812180926.16689-3-andrea.mayer@uniroma2.it
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Hangbin Liu <haliu@redhat.com>

Author: Hangbin Liu

tools/testing/selftests/net/Makefile

@@ -34,6 +34,7 @@ TEST_PROGS += srv6_end_dt6_l3vpn_test.sh
 TEST_PROGS += srv6_hencap_red_l3vpn_test.sh
 TEST_PROGS += srv6_hl2encap_red_l2vpn_test.sh
 TEST_PROGS += srv6_end_next_csid_l3vpn_test.sh
+TEST_PROGS += srv6_end_x_next_csid_l3vpn_test.sh
 TEST_PROGS += srv6_end_flavors_test.sh
 TEST_PROGS += vrf_strict_mode_test.sh
 TEST_PROGS += stress_reuseport_listen.sh