Merge branch 'ip-improve-tcp-sock-multipath-routing'

Willem de Bruijn says:

====================
ip: improve tcp sock multipath routing

From: Willem de Bruijn <willemb@google.com>

Improve layer 4 multipath hash policy for local tcp connections:

patch 1: Select a source address that matches the nexthop device.
         Due to tcp_v4_connect making separate route lookups for saddr
         and route, the two can currently be inconsistent.

patch 2: Use all paths when opening multiple local tcp connections to
         the same ip address and port.

patch 3: Test the behavior. Extend the fib_tests.sh testsuite with one
         opening many connections, and count SYNs on both egress
         devices, for packets matching the source address of the dev.

Changelog in the individual patches
====================

Link: https://patch.msgid.link/20250424143549.669426-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>