Merge branch 'ynl-ethtool-netlink-fix-nla_len-overflow-for-large-string-sets'

Hangbin Liu says:

====================
ynl/ethtool/netlink: fix nla_len overflow for large string sets

This series addresses a silent data corruption issue triggered when ynl
retrieves string sets from NICs with a large number of statistics entries
(e.g. mlx5_core with thousands of ETH_SS_STATS strings).

The root cause is that struct nlattr.nla_len is a __u16 (max 65535
bytes). When a NIC exports enough statistics strings, the
ETHTOOL_A_STRINGSET_STRINGS nest built by strset_fill_set() exceeds
this limit. nla_nest_end() silently truncates the length on assignment,
producing a corrupted netlink message.

Patch 1 moves ethtool.py to selftest.

Patch 2 improves the ethtool tool: rename the doit/dumpit helpers
to do_set/do_get and convert do_get to use ynl.do() with an
explicit device header instead of a full dump with client-side filtering.

Patch 3 adds a --dbg-small-recv option to the YNL ethtool tool,
matching the same option already present in cli.py, to help debug netlink
message size issues

Patch 4 adds a new helper nla_nest_end_safe() to check whether the nla_len
is overflow and return -EMSGSIZE early if so.

Patch 5 uses the new helper in ethtool to make sure the ethtool doesn't
reply a corrupted netlink message.
====================

Link: https://patch.msgid.link/20260408-b4-ynl_ethtool-v2-0-7623a5e8f70b@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>