net: multipath routing: configurable seed

This is the sixth version of the mpath seed series.

This patch series adds ability for a user to assign seed value to multipath route hashes.

changes v6:
- Fix author name and surname position

changes v5:
- patch was splited to patch series
- remove CONFIG_IP_ROUTE_MULTIPATH define from flow_multipath_hash_from_keys(), it used in both IPv4/IPv6 protos.

The mainlining discussion history of this branch:
v5: https://lore.kernel.org/netdev/YIgu4hLNSa69%2FoFZ@rnd/
v4: https://lore.kernel.org/netdev/YILPPCyMjlnhPmEN@rnd/

Pavel Balaev (3):
net/ipv4: multipath routing: configurable seed net/ipv6: multipath routing: configurable seed selftests/net/forwarding: configurable seed tests

 Documentation/networking/ip-sysctl.rst             |  14 +
 include/net/flow_dissector.h                       |   2 +
 include/net/netns/ipv4.h                           |   2 +
 include/net/netns/ipv6.h                           |   3 +
 net/core/flow_dissector.c                          |   7 +
 net/ipv4/route.c                                   |  10 +-
 net/ipv4/sysctl_net_ipv4.c                         |  97 ++++++
 net/ipv6/route.c                                   |  10 +-
 net/ipv6/sysctl_net_ipv6.c                         |  96 ++++++
 tools/testing/selftests/net/forwarding/Makefile    |   1 +
 tools/testing/selftests/net/forwarding/lib.sh      |  28 ++
 .../net/forwarding/router_mpath_seed.sh (new +x)   | 347 +++++++++++++++++++++
 12 files changed, 615 insertions(+), 2 deletions(-)