net: psample: fix info leak in PSAMPLE_ATTR_DATA

net: psample: fix info leak in PSAMPLE_ATTR_DATA

psample open codes nla_put() presumably to avoid wiping
the data with 0s just to override it with packet data.
This open coding is missing clearing the pad, however,
each netlink attr is padded to 4B and data_len may
not be divisible by 4B.

Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://patch.msgid.link/20260616003046.1099490-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>