Merge branch 'net-tcp-make-txhash-use-consistent-for-ipv4'

Antoine Tenart says:

====================
net: tcp: make txhash use consistent for IPv4

Series is divided in two parts. First two commits make the txhash (used
for the skb hash in TCP) to be consistent for all IPv4/TCP packets (IPv6
doesn't have the same issue). Last commit improve a hash-related doc.

One example is when using OvS with dp_hash, which uses skb->hash, to
select a path. We'd like packets from the same flow to be consistent, as
well as the hash being stable over time when using net.core.txrehash=0.
Same applies for kernel ECMP which also can use skb->hash.
====================

Link: https://lore.kernel.org/r/20230523161453.196094-1-atenart@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>