Merge branch 'seg6-headend-reduced'

Andrea Mayer says:

====================
seg6: add support for SRv6 Headend Reduced

This patchset adds support for SRv6 Headend behavior with Reduced
Encapsulation. It introduces the H.Encaps.Red and H.L2Encaps.Red versions
of the SRv6 H.Encaps and H.L2Encaps behaviors, according to RFC 8986 [1].

In details, the patchset is made of:
 - patch 1/4: add support for SRv6 H.Encaps.Red behavior;
 - Patch 2/4: add support for SRv6 H.L2Encaps.Red behavior;
 - patch 2/4: add selftest for SRv6 H.Encaps.Red behavior;
 - patch 3/4: add selftest for SRv6 H.L2Encaps.Red behavior.

The corresponding iproute2 patch for supporting SRv6 H.Encaps.Red and
H.L2Encaps.Red behaviors is provided in a separated patchset.

[1] - https://datatracker.ietf.org/doc/html/rfc8986

V4 -> v5:
 - Fix skb checksum for SRH Reduced encapsulation/insertion;

 - Improve selftests by:
      i) adding a random suffix to network namespaces;
     ii) creating net devices directly into network namespaces;
    iii) using trap EXIT command to properly clean up selftest networks.

 Thanks to Paolo Abeni.

v3 -> v4:
 - Add selftests to the Makefile, thanks to Jakub Kicinski.

v2 -> v3:
 - Keep SRH when HMAC TLV is present;

 - Split the support for H.Encaps.Red and H.L2Encaps.Red behaviors in two
   patches (respectively, patch 1/4 and patch 2/4);

 - Add selftests for SRv6 H.Encaps.Red and H.L2Encaps.Red.

v1 -> v2:
 - Fixed sparse warnings;

 - memset now uses sizeof() instead of hardcoded value;

 - Removed EXPORT_SYMBOL_GPL.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>