Merge branch 'unmask-upper-dscp-bits-part-3'

Merge branch 'unmask-upper-dscp-bits-part-3'

Ido Schimmel says:

====================
Unmask upper DSCP bits - part 3

tl;dr - This patchset continues to unmask the upper DSCP bits in the
IPv4 flow key in preparation for allowing IPv4 FIB rules to match on
DSCP. No functional changes are expected.

The TOS field in the IPv4 flow key ('flowi4_tos') is used during FIB
lookup to match against the TOS selector in FIB rules and routes.

It is currently impossible for user space to configure FIB rules that
match on the DSCP value as the upper DSCP bits are either masked in the
various call sites that initialize the IPv4 flow key or along the path
to the FIB core.

In preparation for adding a DSCP selector to IPv4 and IPv6 FIB rules, we
need to make sure the entire DSCP value is present in the IPv4 flow key.
This patchset continues to unmask the upper DSCP bits, but this time in
the output route path, specifically in the callers of
ip_route_output_ports().

The next patchset (last) will handle the callers of
ip_route_output_key(). Split from this patchset to avoid going over the
15 patches limit.

No functional changes are expected as commit 1fa3314c14c6 ("ipv4:
Centralize TOS matching") moved the masking of the upper DSCP bits to
the core where 'flowi4_tos' is matched against the TOS selector.
====================

Link: https://patch.msgid.link/20240903135327.2810535-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>